fix(security): close critical auth/SSRF/RBAC holes

Verified locally end-to-end (before: exploitable, after: blocked).

- config: refuse to start on weak/default/short SECRET_KEY (was
  trivially forgeable JWT -> full admin)
- deps: add reusable require_admin dependency (JWT or API key)
- api-keys: require admin to mint/list/revoke; mask key on list
  (was unauthenticated -> instant admin API key)
- webhooks: whole router now admin-only (was fully unauthenticated
  CRUD + readable logs)
- webhook delivery: validate URL scheme + reject hosts resolving to
  private/loopback/link-local/reserved IPs; disable redirects
  (was a readable SSRF primitive)
- rbac: implement a real project-role hierarchy in check_project_role
  (was a no-op: any member, even guest, passed admin/mgr gates)
- misc: auth on delete_milestone (+ensure_can_edit_milestone),
  worklog create/delete (force caller user_id, owner-only delete),
  /activity and /export/tasks (were unauthenticated data exposure)
- tasks: auth + ensure_can_edit_task on assign_task and batch_assign

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/api/routers/webhooks.py

@@ -5,11 +5,13 @@ from fastapi import APIRouter, Depends, HTTPException, status, BackgroundTasks
 from sqlalchemy.orm import Session
 
 from app.core.config import get_db
+from app.api.deps import require_admin
 from app.models.webhook import Webhook, WebhookLog
 from app.schemas.webhook import WebhookCreate, WebhookUpdate, WebhookResponse, WebhookLogResponse
 from app.services.webhook import fire_webhooks_sync
 
-router = APIRouter(prefix="/webhooks", tags=["Webhooks"])
+# Webhook management is admin-only (registration, inspection, retry, logs).
+router = APIRouter(prefix="/webhooks", tags=["Webhooks"], dependencies=[Depends(require_admin)])
 
 
 @router.post("", response_model=WebhookResponse, status_code=status.HTTP_201_CREATED)