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/components/Layout.tsx

@@ -183,6 +183,18 @@ function Layout({ children }: LayoutProps) {
                           </svg>
                           SSO Configuration
                         </NavLink>
+                        <NavLink
+                          to="/admin/cache"
+                          className="user-menu-item"
+                          onClick={() => setShowUserMenu(false)}
+                        >
+                          <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
+                            <path d="M21 16V8a2 2 0 0 0-1-1.73l-7-4a2 2 0 0 0-2 0l-7 4A2 2 0 0 0 3 8v8a2 2 0 0 0 1 1.73l7 4a2 2 0 0 0 2 0l7-4A2 2 0 0 0 21 16z"/>
+                            <polyline points="3.27 6.96 12 12.01 20.73 6.96"/>
+                            <line x1="12" y1="22.08" x2="12" y2="12"/>
+                          </svg>
+                          Cache Management
+                        </NavLink>
                       </>
                     )}
                     <div className="user-menu-divider"></div>
@@ -229,7 +241,7 @@ function Layout({ children }: LayoutProps) {
             </svg>
             <span className="footer-logo">Orchard</span>
             <span className="footer-separator">·</span>
-            <span className="footer-tagline">Content-Addressable Storage</span>
+            <span className="footer-tagline">The cache that never forgets</span>
           </div>
           <div className="footer-links">
             <a href="/docs">Documentation</a>