refactor(tool_bias): merge BiasProfile from models.py into tool_bias.py

Per the 4-criteria decision rule: BiasProfile fails C1 (only used by
tool_presets + tool_bias), fails C2 (no state machine), fails C3 (no
dedicated test file), borderline C4. MERGE into the existing
src/tool_bias.py which already has ToolBiasEngine.

This commit:
 1. Adds BiasProfile class definition to src/tool_bias.py at the top
    (after the dataclass + typing imports).
 2. Removes BiasProfile from src/models.py.
 3. Adds lazy re-export via the existing __getattr__ in src/models.py
    (EAGER would deadlock: tool_presets needs BiasProfile + tool_bias
    needs Tool/ToolPreset, and both want models re-exports).
 4. Updates src/tool_presets.py to use the local-import pattern for
    BiasProfile (in load_all_bias_profiles) + adds
    'from __future__ import annotations' so the 'BiasProfile' type
    annotation is a string. This breaks the cycle.
 5. Updates src/tool_bias.py to import Tool + ToolPreset from
    src.tool_presets directly (no longer through models) + adds
    'from __future__ import annotations'.

Verification: VC8 (BiasProfile)
  from src.tool_bias   import BiasProfile        # OK
  from src.tool_presets import Tool, ToolPreset  # OK
  from src.models       import Tool, ToolPreset, BiasProfile  # OK (lazy)
  Tool is Tool returns True
  ToolPreset is ToolPreset returns True
  BiasProfile is BiasProfile returns True

Tests verified (10/10 PASS):
  tests/test_tool_preset_manager.py (4 tests)
  tests/test_bias_models.py (3 tests)
  tests/test_tool_bias.py (3 tests)

Cycle resolution:
  models -> tool_presets (lazy via __getattr__)
  tool_presets -> tool_bias (local import in function body, only at call time)
  tool_bias -> tool_presets (eager; OK because tool_presets is fully
                              loaded by the time tool_bias's class
                              definitions need Tool/ToolPreset)
  The eager load of tool_bias from tool_presets is what made the
  'from __future__ import annotations' necessary in both files (for
  Tool/ToolPreset string annotations in tool_bias method signatures).

src/tool_presets.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import tomllib
 import tomli_w
 
@@ -6,7 +8,6 @@ from pathlib     import Path
 from typing      import Dict, List, Optional, Union, Any
 
 from src               import paths
-from src.models        import BiasProfile
 from src.type_aliases  import Metadata
 
 
@@ -135,10 +136,11 @@ class ToolPresetManager:
    del data["presets"][name]
    self._write_raw(path, data)
 
- def load_all_bias_profiles(self) -> Dict[str, BiasProfile]:
+ def load_all_bias_profiles(self) -> Dict[str, "BiasProfile"]:
   """
   [C: tests/test_tool_preset_manager.py:test_bias_profiles_merged, tests/test_tool_preset_manager.py:test_delete_bias_profile, tests/test_tool_preset_manager.py:test_save_bias_profile]
   """
+  from src.tool_bias import BiasProfile
   global_path = paths.get_global_tool_presets_path()
   global_data = self._read_raw(global_path).get("bias_profiles", {})