Add upstream caching infrastructure and refactor CI pipeline

Upstream Caching (Epic #68-#75, #105):
- Add upstream_sources and cache_settings tables with migrations
- Add cache management API endpoints (CRUD for sources, settings)
- Add environment variable overrides for upstream sources and cache settings
- Add encryption module for storing credentials securely
- Add frontend Admin Cache Management page
- Add is_system field to projects for system cache distinction
- Add purge_seed_data for transitioning to production-like environments

CI Pipeline Refactoring:
- Remove reset jobs (reset_stage_pre, reset_stage)
- Add ephemeral orchard-test deployment for main branch testing
- Run integration tests on ephemeral deployment before promoting to stage
- Stage is now long-running pre-prod (smoke tests only)
- Disable prosper_setup for tag pipelines

frontend/src/App.tsx

@@ -11,6 +11,7 @@ import ChangePasswordPage from './pages/ChangePasswordPage';
 import APIKeysPage from './pages/APIKeysPage';
 import AdminUsersPage from './pages/AdminUsersPage';
 import AdminOIDCPage from './pages/AdminOIDCPage';
+import AdminCachePage from './pages/AdminCachePage';
 import ProjectSettingsPage from './pages/ProjectSettingsPage';
 import TeamsPage from './pages/TeamsPage';
 import TeamDashboardPage from './pages/TeamDashboardPage';
@@ -50,6 +51,7 @@ function AppRoutes() {
                 <Route path="/settings/api-keys" element={<APIKeysPage />} />
                 <Route path="/admin/users" element={<AdminUsersPage />} />
                 <Route path="/admin/oidc" element={<AdminOIDCPage />} />
+                <Route path="/admin/cache" element={<AdminCachePage />} />
                 <Route path="/teams" element={<TeamsPage />} />
                 <Route path="/teams/:slug" element={<TeamDashboardPage />} />
                 <Route path="/teams/:slug/settings" element={<TeamSettingsPage />} />