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.

package-lock.json

@@ -26,6 +26,8 @@
       "name": "@trek/client",
       "version": "3.0.22",
       "dependencies": {
+        "@fontsource/geist-sans": "^5.2.5",
+        "@fontsource/poppins": "^5.2.7",
         "@react-pdf/renderer": "^4.5.1",
         "@trek/shared": "*",
         "axios": "^1.6.7",
@@ -2505,6 +2507,24 @@
         }
       }
     },
+    "node_modules/@fontsource/geist-sans": {
+      "version": "5.2.5",
+      "resolved": "https://registry.npmjs.org/@fontsource/geist-sans/-/geist-sans-5.2.5.tgz",
+      "integrity": "sha512-anllOHyJbElRs9fV15TeDRqAeb1IKm4bSknPl6ZMoyPTx1BBy7logudcUwpNjmQLkzn4Q0JGQLRCUKJYoyST6A==",
+      "license": "OFL-1.1",
+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
+    },
+    "node_modules/@fontsource/poppins": {
+      "version": "5.2.7",
+      "resolved": "https://registry.npmjs.org/@fontsource/poppins/-/poppins-5.2.7.tgz",
+      "integrity": "sha512-6uQyPmseo4FgI97WIhA4yWRlNaoLk4vSDK/PyRwdqqZb5zAEuc+Kunt8JTMcsHYUEGYBtN15SNkMajMdqUSUmg==",
+      "license": "OFL-1.1",
+      "funding": {
+        "url": "https://github.com/sponsors/ayuhito"
+      }
+    },
     "node_modules/@hono/node-server": {
       "version": "1.19.14",
       "license": "MIT",
@@ -5209,6 +5229,7 @@
       "os": [
         "win32"
       ],
+      "peer": true,
       "engines": {
         "node": ">=10"
       }