feat(agents): add crudable skill for CRUDable + permissions guidance

Checklist skill invoked before editing models in pkg/models/. Covers Can*
method placement (on the model, never in route handlers), the four
permission methods, required positive+negative test coverage, and the
anti-patterns most frequently flagged in review.

.claude/skills/crudable/SKILL.md

@@ -0,0 +1,49 @@
+---
+name: crudable
+description: Use when adding or modifying a model in pkg/models/ that needs CRUD operations or permission checks. Covers Can* method placement, CRUDable interface, and required test coverage.
+user-invocable: true
+---
+
+# CRUDable + Permissions
+
+Models in `pkg/models/` that expose CRUD operations must implement the `CRUDable` interface **and** the permission methods. Permissions are enforced at the **model level** via `Can*` methods — never re-checked in route handlers.
+
+**Reference docs:** read `pkg/web/readme.md` for the full interface definitions, DB session semantics, and call order. The interface lives at `pkg/web/web.go`. This skill is a checklist of what the review feedback surfaces on top of that.
+
+## Before writing CRUD or route code
+
+1. Decide which operations the model needs: Read / ReadAll / Create / Update / Delete.
+2. Implement the matching permission methods on the model. Typical signatures:
+   - `CanRead(s *xorm.Session, a web.Auth) (bool, int, error)`
+   - `CanCreate(s *xorm.Session, a web.Auth) (bool, error)`
+   - `CanUpdate(s *xorm.Session, a web.Auth) (bool, error)`
+   - `CanDelete(s *xorm.Session, a web.Auth) (bool, error)`
+3. If a handler or service needs to check access, call the `Can*` method. Do **not** re-implement the check inline or duplicate the logic in `pkg/routes/`.
+4. Do not implement empty stub methods just to satisfy the interface, instead embed the interface in the struct. Check existing models to see how that's done.
+
+Look at `pkg/models/project.go` or `pkg/models/task.go` for reference implementations.
+
+The initial querying of the data should happen in the Can* function. Because we're operating on a pointer, the function that does the work should not need to re-query the model data.
+
+## Anti-patterns (these get flagged every time)
+
+- Permission logic inlined in `pkg/routes/` handlers instead of on the model.
+- Shipping `Create` but forgetting `CanUpdate` / `CanDelete` because "only create is new right now".
+- Re-querying the DB in the handler to decide access — that work belongs in `CanRead`.
+- Copy-pasting permission logic across `CanUpdate` and `CanDelete` — extract a helper.
+- Adding a handler that bypasses the generic CRUD handler in `pkg/web/handler/` without a clear reason (the generic handler already invokes the `Can*` methods for you).
+
+## Tests (mandatory)
+
+Every `Can*` method needs both positive and negative coverage. Run with `mage test:filter <TestName>` while iterating.
+
+- User with direct permission → passes
+- User without permission → denied
+- Permission inherited via parent (e.g., project → task, team → project) → still passes
+- Shared access edge cases (link shares, team membership) if the model supports them
+
+## Related
+
+- Generic CRUD handler: `pkg/web/handler/`
+- Permission type definitions: `pkg/web/auth.go`, `pkg/models/permissions.go`
+- After the model is stable, register the routes in `pkg/routes/api/v1/` and add Swagger annotations. Do not edit `pkg/swagger/` directly — it's generated.