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>

crates/executor-core/src/sandbox.rs

@@ -24,6 +24,12 @@ pub struct Limits {
     /// Max call/expression nesting depth.
     pub max_call_levels: usize,
     pub max_expr_depth: usize,
+
+    /// v1.1.3: hard ceiling on `import` chain depth (A→B→C→…). Independent
+    /// of cycle detection — guards against deep but acyclic graphs.
+    /// Not script-overridable (this is a platform-level guard, not a
+    /// per-script knob).
+    pub module_import_depth_max: u32,
 }
 
 impl Default for Limits {
@@ -35,6 +41,7 @@ impl Default for Limits {
             max_map_size: 10_000,
             max_call_levels: 64,
             max_expr_depth: 64,
+            module_import_depth_max: 8,
         }
     }
 }
@@ -65,6 +72,9 @@ impl Limits {
             max_expr_depth: overrides
                 .max_expr_depth
                 .map_or(self.max_expr_depth, narrow_usize),
+            // module_import_depth_max is platform-level — overrides
+            // never touch it. Carry through unchanged.
+            module_import_depth_max: self.module_import_depth_max,
         }
     }
 }