refactor(consumers): migrate 85 'from src.models import' sites to direct subsystem imports

Per post_module_taxonomy_de_cruft_20260627 Phase 2 (FR7). Each
'from src.models import X' for a moved class is rewritten to
'from src.<destination> import X':

  Ticket, Track, WorkerContext, TrackState, TrackMetadata,
    ThinkingSegment, EMPTY_TRACK_STATE            -> src.mma
  ProjectContext, ProjectMeta, ProjectOutput, ProjectFiles,
    ProjectScreenshots, ProjectDiscussion, EMPTY_PROJECT_CONTEXT -> src.project
  FileItem, Preset, ContextPreset, ContextFileEntry,
    NamedViewPreset                                -> src.project_files
  Tool, ToolPreset                                 -> src.tool_presets
  BiasProfile                                      -> src.tool_bias
  TextEditorConfig, ExternalEditorConfig,
    EMPTY_TEXT_EDITOR_CONFIG                       -> src.external_editor
  Persona                                          -> src.personas
  WorkspaceProfile                                -> src.workspace_manager
  MCPServerConfig, MCPConfiguration, VectorStoreConfig,
    RAGConfig, load_mcp_config                      -> src.mcp_client

NOT touched (kept on src.models; Phase 3 or Phase 4 will move them):
  GenerateRequest, ConfirmRequest, DEFAULT_TOOL_CATEGORIES, Metadata, PROVIDERS

Migration was performed by the one-time script
scripts/tier2/artifacts/post_module_taxonomy_de_cruft_20260627/migrate_imports.py
which uses a class-to-module map and re.sub() to rewrite each
'from src.models import X' line.

Total: 85 import lines rewritten across 71 files.

Note: this commit depends on the v2 SHIPPED work
(origin/tier2/module_taxonomy_refactor_20260627) being merged into
this branch NEXT. On master (without the v2 SHIPPED commits), the
destination modules do not exist and these imports would fail.

src/project_manager.py

@@ -32,7 +32,7 @@ from src.type_aliases import (
 )
 
 if TYPE_CHECKING:
- from src.models import TrackState
+ from src.mma import TrackState
 
 TS_FMT: str = "%Y-%m-%dT%H:%M:%S"
 
@@ -270,7 +270,7 @@ def flat_config(proj: Metadata, disc_name: Optional[str] = None, track_id: Optio
  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
+ from src.project 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", "."))
@@ -321,7 +321,7 @@ def load_track_state(track_id: str, base_dir: Union[str, Path] = ".") -> "TrackS
  Returns empty TrackState (zero-init) if not found.
  [C: tests/test_track_state_persistence.py:test_track_state_persistence]
  """
- from src.models import TrackState, EMPTY_TRACK_STATE
+ from src.mma import TrackState, EMPTY_TRACK_STATE
  state_file = paths.get_track_state_dir(track_id, project_path=str(base_dir)) / 'state.toml'
  if not state_file.exists(): return EMPTY_TRACK_STATE
  try: