feat(web,ui): per-project git provider API base URL overrides

Per provider (github|gitlab|gitea) a project override stored in
~/.config/openchamber/projects/<projectId>.json under gitProviders wins
over the global settings.json value (precedence: project override > global
> built-in default). Server forge routes resolve the override per request
directory (worktree-aware via git-common-dir + containment + path fallback,
60s TTL cache); the override host is also accepted for remote parsing and
client detection. New GET/PUT /api/projects/:projectId/git-providers route;
client openchamberConfig preserves the server-owned gitProviders key;
Projects page gains a Git provider API base URLs section; detection store
hydrates per-project overrides (memory-only, server-authoritative).

packages/ui/src/lib/i18n/messages/de.settings.ts

@@ -1124,6 +1124,9 @@ export const settingsDict = {
   'settings.projects.page.toast.customIconAlreadySet': 'Benutzerdefiniertes Symbol bereits für dieses Projekt festgelegt',
   'settings.projects.page.toast.iconDiscovered': 'Projekt-Symbol gefunden',
   'settings.projects.page.toast.saveFailed': 'Fehler beim Speichern der Projekteinstellungen',
+  'settings.projects.page.gitProviders.title': 'API-Basis-URLs der Git-Anbieter',
+  'settings.projects.page.gitProviders.description': 'Überschreibt die globale API-Basis-URL für dieses Projekt. Ist kein Wert gesetzt, wird die globale Einstellung verwendet.',
+  'settings.projects.page.gitProviders.inheritsGlobal': 'Erbt: {url}',
   'settings.usage.sidebar.title': 'Nutzung',
   'settings.usage.sidebar.total': 'Gesamt {count}',
   'settings.usage.sidebar.actions.toggleAutoRefreshAria': 'Automatisches Aktualisieren umschalten',