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/ai_client.py

@@ -49,7 +49,9 @@ from src.vendor_capabilities import VendorCapabilities, get_capabilities
 # TODO(Ed): Eliminate these?
 from src.events             import EventEmitter
 from src.gemini_cli_adapter import GeminiCliAdapter
-from src.models             import FileItem, ToolPreset, BiasProfile, Tool
+from src.project_files import FileItem
+from src.tool_bias import BiasProfile
+from src.tool_presets import ToolPreset, Tool
 from src.paths              import get_credentials_path
 from src.tool_bias          import ToolBiasEngine
 from src.tool_presets       import ToolPresetManager
@@ -2561,7 +2563,7 @@ def _send_grok(md_content: str, user_message: str, base_dir: str,
    if file_items:
     for fi in file_items:
      if fi.get("is_image") and fi.get("base64_data"):
-      from src.models import FileItem as _FIC
+      from src.project_files import FileItem as _FIC
       fi_item = fi if isinstance(fi, _FIC) else _FIC.from_dict(fi)
       user_content = f"[IMAGE: {fi_item.path or 'attachment'}]\n{user_content}"
    if discussion_history and not history:
@@ -2805,7 +2807,7 @@ def _send_qwen(md_content: str, user_message: str, base_dir: str,
    if file_items:
     for fi in file_items:
      if fi.get("is_image") and fi.get("base64_data"):
-      from src.models import FileItem as _FIC
+      from src.project_files import FileItem as _FIC
       fi_item = fi if isinstance(fi, _FIC) else _FIC.from_dict(fi)
       user_content = f"[IMAGE: {fi_item.path or 'attachment'}]\n{user_content}"
    if discussion_history and not history:
@@ -2898,7 +2900,7 @@ def _send_llama(md_content: str, user_message: str, base_dir: str,
    if file_items:
     for fi in file_items:
      if fi.get("is_image") and fi.get("base64_data"):
-      from src.models import FileItem as _FIC
+      from src.project_files import FileItem as _FIC
       fi_item = fi if isinstance(fi, _FIC) else _FIC.from_dict(fi)
       user_content = f"[IMAGE: {fi_item.path or 'attachment'}]\n{user_content}"
    if discussion_history and not history: