feat(interceptors): §9.4 service interceptors — thin KV allow/deny slice

Smallest honest vertical slice of §9.4: a `[[interceptors]]` block (app OR
group) binds a script to run BEFORE `kv::set`/`delete`; it reads the operation
context (`ctx.request.body`: service, action, collection, key, value, caller
ids) and returns `#{ allowed, reason }` — `allowed == false` denies the op (the
write never runs, the caller gets a runtime error).

Reuses two existing mechanisms rather than inventing new ones:
- Registration mirrors extension points (§5.5): a marker table
  `0073_interceptors.sql` (owner-polymorphic app_id/group_id XOR, keyed
  (service, op) → script), `interceptor_repo` (insert/delete/list + the
  nearest-owner-wins `resolve_before` chain walk), reconciled through the
  declarative apply exactly like `vars` (create/update/delete, prunable).
- Execution reuses the `invoke()` re-entry path: the new `InterceptorService`
  (shared trait + Postgres-backed impl) only RESOLVES the script name (keeping
  executor-core Postgres-free); the executor's `sdk::interceptor::run_before`
  resolves that name and runs it via `run_resolved_blocking` (extracted from
  `invoke_blocking` — shared depth bound + AST cache). An un-hooked write pays
  one indexed `Ok(None)` resolve; no interceptor ⇒ zero overhead.

Nearest-owner-wins so an app overrides a group's interceptor, and a group
interceptor is inherited by every descendant app — the chain walk is the
isolation boundary (a sibling subtree never matches). `validate_bundle_for`
restricts the MVP to `service = "kv"`, `op ∈ {set, delete}`, one marker per
(service, op).

Deferred (documented in §9.4): the `data` transform return, services other
than kv, `after_*` hooks, chaining + circular-dependency guard, the timeout
policy, and a `pic interceptors ls` read surface (needs a server route).

Pinned by `tests/interceptors.rs` (deny blocks the write; allow passes;
group→app inheritance), schema snapshot re-blessed. 154/154 journeys pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/picloud/src/lib.rs

@@ -416,6 +416,11 @@ pub async fn build_app(
     let workflow: Arc<dyn picloud_shared::WorkflowService> = Arc::new(
         picloud_manager_core::WorkflowServiceImpl::new(pool.clone()).with_authz(authz.clone()),
     );
+    // §9.4 interceptors: resolve-only (which script guards a kv op); running it
+    // reuses the invoke() re-entry path.
+    let interceptors: Arc<dyn picloud_shared::InterceptorService> = Arc::new(
+        picloud_manager_core::interceptor_service::InterceptorServiceImpl::new(pool.clone()),
+    );
     let services = Services::new(
         kv,
         docs,
@@ -437,7 +442,8 @@ pub async fn build_app(
     .with_group_files(group_files)
     .with_group_pubsub(group_pubsub)
     .with_group_queue(group_queue)
-    .with_workflow(workflow);
+    .with_workflow(workflow)
+    .with_interceptors(interceptors);
     // v1.1.9: keep the invoke depth bound aligned with the dispatcher's
     // trigger-depth bound (same counter under the hood).
     let engine_limits = Limits {