feat(models,project_manager): add ProjectContext + 5 sub-dataclasses (Phase 2 / VC8)

Phase 2: Fix flat_config to return typed ProjectContext (FR8 / VC8)
Before: def flat_config(...) -> Metadata  (returned dict[str, Any])
After:  def flat_config(...) -> ProjectContext  (typed fat struct)
Delta:  -1 anonymous dict return type; +6 new dataclasses

Per SPEC_CORRECTION_phase_2.md, this is Option A (incremental):
- Add 6 sub-dataclasses: ProjectMeta, ProjectOutput, ProjectFiles,
  ProjectScreenshots, ProjectDiscussion, ProjectContext
- Each matches the nested dict shape of flat_config()'s actual return
- ProjectContext has dict-compat methods (__getitem__ + get) so
  consumers using .get() / [] continue to work unchanged
- ProjectContext.to_dict() returns the legacy dict shape for migration
- EMPTY_PROJECT_CONTEXT sentinel exported

File locations per spec:
- src/models.py: 6 new dataclasses + EMPTY_PROJECT_CONTEXT sentinel
- src/project_manager.py: flat_config body rewritten to construct
  ProjectContext from the proj dict (typed return type)
- tests/test_project_context_20260627.py: NEW regression-guard test file
  with 10 tests covering: imports, return type, zero defaults, full
  input, dict-compat __getitem__/get, to_dict round-trip, sentinel,
  output_dir required field, consumer patterns unchanged

Verification:
- audit_weak_types --strict: OK (96 <= 112 baseline; down from 107)
- generate_type_registry: 23 files regenerated
- 10 test_project_context_20260627 tests PASS
- All existing consumer tests pass (test_context_composition_decoupled: 2,
  test_orchestrator_pm: 3, test_orchestration_logic: 8,
  test_orchestrator_pm_history + test_context_preview_button: 7,
  test_project_manager_tracks: 4, test_track_state_persistence: 1)

VC8 (corrected) verification:
- flat_config returns ProjectContext (typed) ✓
- All 6 sub-dataclasses exist + importable ✓
- Dict-compat methods (ctx["key"], ctx.get("key")) work ✓
- output_dir REQUIRED field defaults to "" (empty, but valid) ✓
- Consumer patterns (ctx.get("output", {}).get("namespace", "project"))
  work unchanged via dict-compat ✓

Phase 2 IS COMPLETE.

src/project_manager.py

@@ -265,8 +265,12 @@ def migrate_from_legacy_config(cfg: Metadata) -> Metadata:
  return proj
  # ── flat config for aggregate.run() ─────────────────────────────────────────
 
-def flat_config(proj: Metadata, disc_name: Optional[str] = None, track_id: Optional[str] = None) -> Metadata:
- """Return a flat config dict compatible with aggregate.run()."""
+def flat_config(proj: Metadata, disc_name: Optional[str] = None, track_id: Optional[str] = None) -> "ProjectContext":
+ """Return a typed ProjectContext compatible with aggregate.run().
+ The returned dataclass supports dict-compat (__getitem__ / get) so
+ existing consumers using .get() and [] continue to work unchanged
+ (Phase 2 Option A per SPEC_CORRECTION_phase_2.md)."""
+ from src.models import ProjectContext, ProjectMeta, ProjectOutput, ProjectFiles, ProjectScreenshots, ProjectDiscussion
  disc_sec = proj.get("discussion", {})
  if track_id:
   history = load_track_history(track_id, proj.get("files", {}).get("base_dir", "."))
@@ -274,17 +278,30 @@ def flat_config(proj: Metadata, disc_name: Optional[str] = None, track_id: Optio
   name      = disc_name or disc_sec.get("active", "main")
   disc_data = disc_sec.get("discussions", {}).get(name, {})
   history   = disc_data.get("history", [])
- return {
-  "project":         proj.get("project", {}),
-  "output":          proj.get("output", {}),
-  "files":           proj.get("files",  {}),
-  "screenshots":     proj.get("screenshots", {}),
-  "context_presets": proj.get("context_presets", {}),
-  "discussion":      {
-   "roles":   disc_sec.get("roles", []),
-   "history": history,
-  },
- }
+ return ProjectContext(
+  project=ProjectMeta(
+   name=proj.get("project", {}).get("name", ""),
+   summary_only=proj.get("project", {}).get("summary_only", False),
+   execution_mode=proj.get("project", {}).get("execution_mode", "standard"),
+  ),
+  output=ProjectOutput(
+   namespace=proj.get("output", {}).get("namespace", "project"),
+   output_dir=proj.get("output", {}).get("output_dir", ""),
+  ),
+  files=ProjectFiles(
+   base_dir=proj.get("files", {}).get("base_dir", ""),
+   paths=tuple(proj.get("files", {}).get("paths", [])),
+  ),
+  screenshots=ProjectScreenshots(
+   base_dir=proj.get("screenshots", {}).get("base_dir", "."),
+   paths=tuple(proj.get("screenshots", {}).get("paths", [])),
+  ),
+  context_presets=dict(proj.get("context_presets", {})),
+  discussion=ProjectDiscussion(
+   roles=tuple(disc_sec.get("roles", [])),
+   history=tuple(history),
+  ),
+ )
  # ── track state persistence ─────────────────────────────────────────────────
 
 def save_track_state(track_id: str, state: 'TrackState', base_dir: Union[str, Path] = ".") -> None: