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/web/server/lib/opencode/feature-routes-runtime.js

@@ -7,6 +7,7 @@ import { registerGitHubRoutes } from '../github/routes.js';
 import { registerGitLabRoutes } from '../gitlab/routes.js';
 import { registerGiteaRoutes } from '../gitea/routes.js';
 import { registerGitRoutes } from '../git/routes.js';
+import { registerGitProviderRoutes } from '../git-providers/routes.js';
 import { registerDevServerRoutes } from '../dev-servers/routes.js';
 import { registerMagicPromptRoutes } from '../magic-prompts/routes.js';
 import { registerSessionFoldersRoutes } from '../session-folders/routes.js';
@@ -301,6 +302,7 @@ export const createFeatureRoutesRuntime = (dependencies) => {
     registerGitHubRoutes(app);
     registerGitLabRoutes(app);
     registerGiteaRoutes(app);
+    registerGitProviderRoutes(app);
     registerGitRoutes(app);
     registerDevServerRoutes(app, { scanner: devServerScanner, getOwnPorts });
     registerMagicPromptRoutes(app, {