feat(v0.8.44): P0 state root migration to ~/.codewhale with legacy compat

#2011: migrate app state to ~/.codewhale
- Add CodeWhalePaths: codewhale_home(), legacy_deepseek_home(),
  resolve_state_dir(), ensure_state_dir() in codewhale-config
- Config: resolve_config_path supports CODEWHALE_CONFIG_PATH env,
  default_config_path prefers ~/.codewhale/config.toml
- Project overlay: checks .codewhale/config.toml before .deepseek/
- Sessions: default_sessions_dir uses resolve_state_dir with fallback
- Workspace trust: writes to CodeWhale home via ensure_state_dir
- Init: ensure_deepseek_gitignored adds both .codewhale/ and .deepseek/
- .gitignore: adds .codewhale/

#2010: session artifact hygiene
- /save without path now writes to managed sessions dir instead of cwd
- Boot-time session prune via cleanup_old_sessions (MAX_SESSIONS=50)
- sessions_dir() public accessor for checkpoint path resolution

Fix: load_recent_checkpoint now uses manager.sessions_dir() instead
of hardcoding ~/.deepseek/sessions/checkpoints/

.gitignore

@@ -64,6 +64,7 @@ project_overhaul_prompt.md
 .wrangler/
 
 # Local runtime state
+.codewhale/
 .deepseek/
 **/session_*.json
 *.db