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.

Generated with [Devin](https://devin.ai)

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

Generated with [Devin](https://devin.ai)

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.

Generated with [Devin](https://devin.ai)

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

* 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

Generated with [Devin](https://devin.ai)

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

---------

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

app/backend/internal/api/git_receiver.go

@@ -113,6 +113,26 @@ func handleGitWebhookPush(c *gin.Context) {
 		return
 	}
 
+	engineValue, _ := c.Get("deployment_engine")
+	engine, _ := engineValue.(*deployment.DeploymentEngine)
+
+	enqueued, err := dispatchPushToServices(c, db, engine, cloneURL, fullName, branch, commit, repoUserID)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to match services"})
+		return
+	}
+
+	c.JSON(http.StatusAccepted, gin.H{
+		"received":    true,
+		"branch":      branch,
+		"deployments": enqueued,
+	})
+}
+
+// dispatchPushToServices enqueues a deployment for every service tracking
+// the pushed repo+branch. Shared by the per-repo webhook receiver and the
+// GitHub App webhook endpoint.
+func dispatchPushToServices(c *gin.Context, db *database.DB, engine *deployment.DeploymentEngine, cloneURL, fullName, branch, commit, repoUserID string) (int, error) {
 	rows, err := db.Query(`
 		SELECT s.id, s.project_id, s.name, s.type, s.status, s.image, s.command,
 		       s.environment, s.git_repo, s.git_branch, s.build_path, s.cpu, s.memory,
@@ -121,8 +141,7 @@ func handleGitWebhookPush(c *gin.Context) {
 		WHERE s.git_branch = $1 AND (s.git_repo = $2 OR s.git_repo = $3)`,
 		branch, cloneURL, fullName)
 	if err != nil {
-		c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to match services"})
-		return
+		return 0, err
 	}
 	defer rows.Close()
 
@@ -134,15 +153,11 @@ func handleGitWebhookPush(c *gin.Context) {
 			&s.Environment, &s.GitRepo, &s.GitBranch, &s.BuildPath, &s.CPU, &s.Memory,
 			&s.CreatedAt, &s.UpdatedAt,
 		); err != nil {
-			c.JSON(http.StatusInternalServerError, gin.H{"error": "Failed to scan service"})
-			return
+			return 0, err
 		}
 		services = append(services, s)
 	}
 
-	engineValue, _ := c.Get("deployment_engine")
-	engine, _ := engineValue.(*deployment.DeploymentEngine)
-
 	enqueued := 0
 	for _, service := range services {
 		now := time.Now()
@@ -199,12 +214,7 @@ func handleGitWebhookPush(c *gin.Context) {
 		}
 		enqueued++
 	}
-
-	c.JSON(http.StatusAccepted, gin.H{
-		"received":    true,
-		"branch":      branch,
-		"deployments": enqueued,
-	})
+	return enqueued, nil
 }
 
 // verifyGitWebhookSignature checks the push signature per provider: