feat(costs): rework Budget into Costs — Splitwise-style, multi-currency, mobile (#1106)

* fix(journey): authorize reads of the journey share link

GET /api/journeys/:id/share-link now requires journey access (canAccessJourney),
matching the create/delete share-link routes and the get_journey_share_link MCP
tool. Returns no link when the caller lacks access to the journey.

* feat(costs): rework Budget into Costs — Splitwise-style, multi-currency, mobile

Renames the Budget addon to "Costs" (UI only) and reworks it into a Tricount/
Splitwise-style cost tracker: multiple payers per expense, equal split across
chosen members, settle-up with persisted history + undo, 12 fixed categories,
per-expense currency with live FX conversion to a user-set display currency
(Settings -> Display), and locale-correct money formatting. Adds a desktop and a
dedicated mobile layout. A migration backfills existing budget items (single
payer, split members, currency). Closes #551 (per-expense currency).

Also switches the app font to self-hosted Poppins (Geist for secondary subtext),
replacing the Google Fonts CDN dependency.

* fix(costs): neutral dashboard dark palette + liquid glass, full page width, entry-count badge

- Dark mode used a warm oklch palette that read brownish; switch to the
  neutral zinc tokens used by the dashboard (#121215 bg, #f4f4f5 ink) and add a
  subtle backdrop-blur glass on cards.
- Costs now uses the full available page width on desktop instead of a 1280px cap.
- Render the expense count next to the Expenses title as a badge.
- Adapt budget/journey unit tests to the new payer-based settlement model and the
  Costs rename (category default 'other', Costs tab/CostsPanel).

* fix(costs): drop the entry-count badge, always show row edit/delete actions

Removes the count badge next to the Expenses title and makes the per-row
edit/delete actions permanently visible (no longer hover-only) on desktop too.

* feat(costs): currency-native money formatting, custom select/date, rename addon to Costs

- Format every amount in its own currency convention (symbol position, grouping
  and decimal separators) regardless of app language, via a currency->locale map
  (EUR -> '12,00 €', USD -> '$12.00', JPY -> '¥12', ...). Previously Intl used the
  app locale, so EUR showed the symbol in front under an English UI.
- Use TREK's CustomSelect (searchable, with symbols) and CustomDatePicker in the
  add/edit expense modal instead of the native <select>/<input type=date>.
- Rename the 'Budget Planner' add-on to 'Costs' in the admin list (display only;
  id/tables/permissions/MCP stay 'budget') via seed + a migration for existing DBs.

* feat(auth): configurable session duration via SESSION_DURATION

Adds a SESSION_DURATION env var (ms-style strings: 1h, 7d, 30d, ...) controlling
how long a session stays valid before re-login. It drives both the trek_session
JWT exp claim and the cookie maxAge from one source, so they never drift. Invalid
values warn at startup and fall back to the default (24h — unchanged). The MFA
challenge token and MCP OAuth tokens keep their own TTL.

Implements the request from discussion #946. Documented in the env-var wiki page,
.env.example and docker-compose.yml.

client/src/components/Planner/BookingImportModal.tsx

@@ -194,7 +194,7 @@ export default function BookingImportModal({ isOpen, onClose, tripId, pushUndo }
       <div
         onClick={e => e.stopPropagation()}
         className="bg-surface-card"
-        style={{ borderRadius: 16, width: '100%', maxWidth: 540, padding: 24, boxShadow: '0 8px 32px rgba(0,0,0,0.2)', fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif", maxHeight: '90vh', display: 'flex', flexDirection: 'column' }}
+        style={{ borderRadius: 16, width: '100%', maxWidth: 540, padding: 24, boxShadow: '0 8px 32px rgba(0,0,0,0.2)', fontFamily: "var(--font-system)", maxHeight: '90vh', display: 'flex', flexDirection: 'column' }}
       >
         {/* Header */}
         <div style={{ display: 'flex', alignItems: 'center', gap: 8, marginBottom: 14 }}>

client/src/components/Planner/DayDetailPanel.tsx

@@ -94,7 +94,7 @@ export default function DayDetailPanel({ day, days, places, categories = [], tri
   ) : null
 
   const placesWithCoords = places.filter(p => p.lat && p.lng)
-  const font = { fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif" }
+  const font = { fontFamily: "var(--font-system)" }
 
   return (
     <div className="fixed z-50" style={{ bottom: 'calc(var(--bottom-nav-h) + 20px)', left: `calc(${leftWidth}px + (100vw - ${leftWidth}px - ${rightWidth}px) / 2)`, transform: 'translateX(-50%)', width: `min(800px, calc(100vw - ${leftWidth}px - ${rightWidth}px - 32px))`, ...(mobile ? { zIndex: 10000 } : null), ...font }}>

client/src/components/Planner/DayPlanSidebar.tsx

@@ -1068,7 +1068,7 @@ const DayPlanSidebar = React.memo(function DayPlanSidebar(props: DayPlanSidebarP
     anyGeoPlace,
   } = S
   return (
-    <div style={{ display: 'flex', flexDirection: 'column', height: '100%', position: 'relative', fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif" }}>
+    <div style={{ display: 'flex', flexDirection: 'column', height: '100%', position: 'relative', fontFamily: "var(--font-system)" }}>
       {/* Toolbar */}
       <DayPlanSidebarToolbar
         tripId={tripId}

client/src/components/Planner/FileImportModal.tsx

@@ -224,7 +224,7 @@ export default function FileImportModal({ isOpen, onClose, tripId, pushUndo, ini
       <div
         onClick={e => e.stopPropagation()}
         className="bg-surface-card"
-        style={{ borderRadius: 16, width: '100%', maxWidth: 520, padding: 24, boxShadow: '0 8px 32px rgba(0,0,0,0.2)', fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif" }}
+        style={{ borderRadius: 16, width: '100%', maxWidth: 520, padding: 24, boxShadow: '0 8px 32px rgba(0,0,0,0.2)', fontFamily: "var(--font-system)" }}
       >
         <div style={{ fontSize: 15, fontWeight: 700, color: 'var(--text-primary)', marginBottom: 6 }}>
           {t('places.importFile')}

client/src/components/Planner/PlaceInspector.tsx

@@ -197,7 +197,7 @@ export default function PlaceInspector({
         transform: 'translateX(-50%)',
         width: `min(800px, calc(100% - ${leftWidth}px - ${rightWidth}px - 32px))`,
         zIndex: 50,
-        fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif",
+        fontFamily: "var(--font-system)",
       }}
     >
       <div className="bg-surface-elevated" style={{

client/src/components/Planner/PlacesSidebar.tsx

@@ -23,7 +23,7 @@ const PlacesSidebar = React.memo(function PlacesSidebar(props: PlacesSidebarProp
       onDragOver={handleSidebarDragOver}
       onDragLeave={handleSidebarDragLeave}
       onDrop={handleSidebarDrop}
-      style={{ display: 'flex', flexDirection: 'column', height: '100%', fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif", position: 'relative' }}
+      style={{ display: 'flex', flexDirection: 'column', height: '100%', fontFamily: "var(--font-system)", position: 'relative' }}
     >
       {sidebarDragOver && <PlacesDropOverlay {...S} />}
       {/* Kopfbereich */}

client/src/components/Planner/ReservationsPanel.tsx

@@ -519,7 +519,7 @@ export default function ReservationsPanel({ tripId, reservations, days, assignme
   }, [reservations])
 
   return (
-    <div style={{ height: '100%', display: 'flex', flexDirection: 'column', fontFamily: "-apple-system, BlinkMacSystemFont, 'SF Pro Text', system-ui, sans-serif" }}>
+    <div style={{ height: '100%', display: 'flex', flexDirection: 'column', fontFamily: "var(--font-system)" }}>
       {/* Unified toolbar */}
       <div style={{ padding: '24px 28px 0' }} className="max-md:!px-4 max-md:!pt-4">
         <div className="bg-surface-tertiary" style={{