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/Journey/JourneyMap.tsx

@@ -77,7 +77,7 @@ function markerSvg(dayColor: string, dayLabel: number, highlighted: boolean): st
     <svg width="${MARKER_W}" height="${MARKER_H}" viewBox="0 0 28 36" fill="none" xmlns="http://www.w3.org/2000/svg">
       <path d="M14 34C14 34 26 22.36 26 13C26 6.37 20.63 1 14 1C7.37 1 2 6.37 2 13C2 22.36 14 34 14 34Z" fill="${dayColor}" stroke="${stroke}" stroke-width="1.5"/>
       <circle cx="14" cy="13" r="8" fill="${dayColor}"/>
-      <text x="14" y="13" text-anchor="middle" dominant-baseline="central" fill="#fff" font-family="-apple-system,system-ui,sans-serif" font-size="11" font-weight="700">${label}</text>
+      <text x="14" y="13" text-anchor="middle" dominant-baseline="central" fill="#fff" font-family="'Poppins',system-ui,sans-serif" font-size="11" font-weight="700">${label}</text>
     </svg>
   </div>`
 }

client/src/components/Journey/JourneyMapGL.tsx

@@ -104,7 +104,7 @@ function ensureJourneyPopupStyle() {
       -webkit-backdrop-filter: blur(16px) saturate(180%);
       border: 1px solid rgba(0, 0, 0, 0.06);
       box-shadow: 0 10px 32px rgba(0, 0, 0, 0.18), 0 2px 6px rgba(0, 0, 0, 0.06);
-      font-family: -apple-system, system-ui, sans-serif;
+      font-family:var(--font-system);
       min-width: 160px;
       max-width: 280px;
     }
@@ -185,7 +185,7 @@ function markerHtml(dayColor: string, dayLabel: number, highlighted: boolean): H
   inner.innerHTML = `<svg width="${MARKER_W}" height="${MARKER_H}" viewBox="0 0 28 36" fill="none" xmlns="http://www.w3.org/2000/svg">
     <path d="M14 34C14 34 26 22.36 26 13C26 6.37 20.63 1 14 1C7.37 1 2 6.37 2 13C2 22.36 14 34 14 34Z" fill="${fill}" stroke="${stroke}" stroke-width="1.5"/>
     <circle cx="14" cy="13" r="8" fill="${fill}"/>
-    <text x="14" y="13" text-anchor="middle" dominant-baseline="central" fill="${textColor}" font-family="-apple-system,system-ui,sans-serif" font-size="11" font-weight="700">${label}</text>
+    <text x="14" y="13" text-anchor="middle" dominant-baseline="central" fill="${textColor}" font-family="'Poppins',system-ui,sans-serif" font-size="11" font-weight="700">${label}</text>
   </svg>`
   wrap.appendChild(inner)
   return wrap