feat(git): GitHub App manifest self-provisioning + app-level webhook (#44)

* feat(branding): white-label — public /branding, admin write, shell theming

app_settings branding.* keys (product name, logo/favicon URLs, accent
color, docs/support links). Public GET /branding so login and shell
theme pre-auth; admin writes via PUT /settings.

useBranding() applies document.title, accent CSS var and favicon;
BrandWordmark replaces hardcoded wordmarks; admin Platform settings
gain a Branding form. MCP containr_branding_get + settings_update.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(invites): team invite links — admin create/revoke, public accept

Admins mint single-use invite links (sha256-hashed token at rest,
optional email binding, configurable TTL). Public endpoints let the
accept page validate the link and register — working even while
public signup is disabled.

- migration + sqlc queries/model for user_invites
- POST /admin/invites (returns one-time token+url), GET list, DELETE revoke
- GET /auth/invites/:token public validation, POST /auth/accept-invite
- CLI containr invites list|create|revoke; MCP invites tools
- /auth/accept-invite page (expired/used/invalid states, bound-email lock)
- Admin page Team invites section: create, copy link, revoke
- OpenAPI + generated types + CLI guide

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* feat(admin): impersonate user — 15-min token, audit-logged

POST /admin/users/:id/impersonate mints a short-lived bearer token
(impersonated_by claim) for support/debugging. Admin accounts cannot
be impersonated; every mint is audit-logged with actor + target.

- CLI: containr admin impersonate <user-id> (works via CONTAINR_TOKEN)
- MCP: containr_admin_impersonate
- Admin UI: per-user Impersonate action → token modal with usage hint
- OpenAPI + generated types

Verified live: token resolves to target, admin target 403, audit row.

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* feat(git): GitHub App manifest self-provisioning + app-level webhook

Admins create the instance GitHub App in-browser instead of hand-
setting GITHUB_APP_* env vars:

- POST /admin/git/github-app/manifest builds the manifest + URL;
  the frontend auto-submits it to github.com
- /git/github-app/callback page exchanges the code via
  POST /admin/git/github-app/convert; credentials persist in
  app_settings (precedence over env)
- GET /admin/git/github-app reports configured/source
- POST /api/git/github-app/webhook — single app-level push receiver,
  HMAC-verified, dispatches via extracted dispatchPushToServices
- install-url + installation-token paths resolve settings→env
- CLI: containr admin github-app status|manifest|convert; MCP tools
- Git providers UI shows "Set up GitHub App" for admins when
  unconfigured

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---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

ROADMAP2.md

@@ -310,10 +310,19 @@ and wired refs, one click or one CLI call.
   `POST /auth/accept-invite` registers — works while public signup is
   closed. `/auth/accept-invite` page, admin manage/revoke UI,
   `containr invites` CLI + MCP tools.
-- [ ] **Impersonate user** — admin support tool, audit-logged.
-- [ ] **GitHub App manifest flow** — `POST /git/github-app/manifest`
-  returns manifest + redirect; instance self-provisions its App
-  (dflow pattern — removes the env-setup barrier).
+- [x] **Impersonate user** — `POST /admin/users/:id/impersonate`
+  mints a 15-minute bearer token (`impersonated_by` claim),
+  audit-logged; admin accounts are not impersonatable. CLI
+  `admin impersonate`, MCP tool, admin UI token modal. Remaining:
+  in-browser session swap needs a session bridge.
+- [x] **GitHub App manifest flow** — `POST /admin/git/github-app/manifest`
+  returns manifest + submission URL; the callback page exchanges
+  `code` via `POST /admin/git/github-app/convert` and credentials
+  persist in `app_settings` (overriding `GITHUB_APP_*` env). New
+  public `POST /api/git/github-app/webhook` receives App-level push
+  events (HMAC-verified) and enqueues matching services. Settings→env
+  fallback wired into install-URL + installation-token paths.
+  `containr admin github-app` CLI + MCP + OpenAPI.
 - [ ] **fork-sync trigger** — accept repo-sync events on webhook
   receiver.
 - [ ] **Dynamic filter framework** — port dflow's `filter.utils`