feat(v1.1.3-modules): shared types, migrations, engine + resolver scaffold

Lays down the v1.1.3 plumbing:

- `ScriptKind` enum in `picloud-shared` ('endpoint' | 'module').
- `ModuleSource` trait + `ModuleScript` DTO + `NoopModuleSource` in
  `picloud-shared`. Resolver lives in `executor-core`; Postgres impl
  in `manager-core` (`PostgresModuleSource`).
- `Services::new` grows a fifth `modules: Arc<dyn ModuleSource>` arg.
- `ScriptValidator` returns `ValidatedScript { imports }` so the
  manager can populate the dep-graph table on save. New
  `validate_module` method on the trait gates module-shape rules.
- `Engine::execute_ast(&Arc<rhai::AST>, req)` lets the orchestrator's
  script cache reuse compiled ASTs. `Engine::execute(&str, req)` is
  preserved as a convenience that compiles inline. `Engine::compile`
  exposes the AST for callers that want to cache.
- `PicloudModuleResolver` replaces `DummyModuleResolver` per-call.
  Bridges Rhai's sync `ModuleResolver::resolve` to async
  `ModuleSource::lookup` via `Handle::block_on`. Enforces:
  - cross-app isolation (resolver captures `Arc<SdkCallCx>`),
  - circular import detection (in-progress stack on the resolver),
  - import depth limit (default 8 via
    `Limits::module_import_depth_max`).
- Module-shape validation walks `ast.statements()` via `rhai/internals`
  and accepts only `Var { CONSTANT }`, `Import`, and `Noop`. The
  manager admin endpoint runs `validate_module` at save (primary
  gate); resolver re-runs it at load (defense in depth).
- LRU cache `(AppId, name) -> (updated_at, Arc<Module>)` owned by
  `Engine`. Size from `PICLOUD_MODULE_CACHE_SIZE` (default 512).
- Migration `0015_scripts_kind.sql` adds `scripts.kind` + composite
  index + module-name shape CHECK.
- Migration `0016_script_imports.sql` adds the dep-graph table with
  FK CASCADE on both columns.
- Repo: `kind` threaded through SELECT/INSERT/UPDATE. New
  `count_routes_for_script` / `count_triggers_for_script` /
  `list_imports` methods. `create`/`update` open a transaction and
  call `replace_imports_tx` to populate the dep-graph.
- Admin endpoint: accepts `kind`; rejects reserved module names;
  rejects `endpoint → module` transitions when routes / triggers
  exist.
- SDK_VERSION 1.3 → 1.4.

Workspace builds; full test suite (~440 tests) green.

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

Cargo.lock

@@ -1274,6 +1274,15 @@ version = "0.4.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5e5032e24019045c762d3c0f28f5b6b8bbf38563a65908389bf7978758920897"
 
+[[package]]
+name = "lru"
+version = "0.12.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "234cf4f4a04dc1f57e24b96cc0cd600cf2af460d4161ac5ecdd0af8e1f3b2a38"
+dependencies = [
+ "hashbrown 0.15.5",
+]
+
 [[package]]
 name = "lru-slab"
 version = "0.1.2"
@@ -1570,6 +1579,7 @@ dependencies = [
  "base64",
  "chrono",
  "hex",
+ "lru",
  "percent-encoding",
  "picloud-shared",
  "rand 0.8.6",