refactor(app_controller): remove redundant hasattr(f, ...) defensive checks

Phase 3 (partial): self.files guarantee (FR4 row 1)
Before: 13 hasattr(f, ...) defensive checks in src/app_controller.py
After:  0 (self.files is GUARANTEED List[FileItem] per init at 1996-2005)
Delta:  -13 sites

Per the spec's FR4 row 1: 'After Phase 3, self.files is GUARANTEED
List[FileItem]. Every hasattr(f, "path") check is redundant. Remove it.'

The init code at src/app_controller.py:1996-2005 already does the correct
isinstance check + FileItem.from_dict() pattern, so all 13 hasattr checks
on self.files / self.context_files are redundant defensive code.

Verification:
- audit_weak_types --strict: OK (107 <= 112 baseline)
- py_check_syntax src/app_controller.py: OK
- 59 tests pass (type_aliases, openai_schemas, rag_engine, file_item, etc.)

OUT OF SCOPE (deferred):
- 18 hasattr(f, 'path') checks in src/gui_2.py (Phase 3 follow-up)
- Phase 4: _do_generate return type
- Phase 5: rag_engine.search() return type
- Phase 6: 30 Optional[T] returns
- Phase 7: 59 Any params + 10 dict[str, Any] params
See TRACK_COMPLETION_cruft_elimination_20260627.md for full scope.

conductor/tracks/cruft_elimination_20260627/plan.md

@@ -67,6 +67,8 @@ print('all from_dict methods:', all(hasattr(c, 'from_dict') for c in [CommsLogEn
 
 ## §Phase 1: Promote `Metadata` from `TypeAlias = dict[str, Any]` to a typed fat struct
 
+> **[x] COMPLETE** [commit 75eb6dbb] — Metadata is now `@dataclass(frozen=True, slots=True)` with 36 explicit fields; `Metadata: TypeAlias = dict[str, Any]` removed. Dict-compat methods (`__getitem__`, `get`, `__contains__`, `__iter__`, `keys`, `values`, `items`) keep existing call sites working during the migration. 133 tests pass; audit_weak_types --strict OK (107 <= 112).
+
 **WHERE:** `src/type_aliases.py:6`
 
 **Current state (line 6):**