Navi Code: stop via Esc + project cwd propagation ...

- TUI: Esc stops active stream cooperatively via POST /sessions/{id}/stop
- TUI: render stream_stopped as status message
- CLI/WebSocket: send shell cwd in client->server message field
- Orchestrator stores cwd in session.session_metadata
- ContextBuilder injects [Working directory] into LLM context
- Agent sets current_working_directory ContextVar per turn
- tools/base: ToolContext gains cwd field
- filesystem/terminal/code_exec resolve relative paths against session cwd
- Add bin/navi-code wrapper for PATH symlink; document in README.md
- Update docs/websocket.md and tests

Full pytest: 544 passed, 1 skipped.

Co-Authored-By: Claude <noreply@anthropic.com>

Pass explicit ToolContext to tools instead of hidden ContextVars ...

Add ToolContext dataclass (session_id, event_sink, stop_event, model,
user_id, user_role, user_info) and thread it through the execution chain:
Agent._execute_tools_with_sink → ToolExecutor → tool.execute().

All ~25 tools updated to accept ctx parameter. Tools that previously
read ContextVar now prefer ctx when provided, falling back to
ContextVar for backward compatibility.

Tests updated to pass ToolContext explicitly — no more test fixtures
that set current_session_id / current_user_id ContextVars.

ContextVar setters remain as fallback for non-tool consumers
(ai_helper, context_builder, planning) and will be removed in a
follow-up refactor.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Refactor: move tool helper modules into _internal subpackage ...

Moves non-tool infrastructure out of navi/tools/ root so that only
actual tool classes live there:

  base.py           → _internal/base.py
  loader.py         → _internal/loader.py
  middleware.py     → _internal/middleware.py
  logging_middleware.py → _internal/logging_middleware.py
  _time_parser.py   → _internal/time_parser.py

All imports updated across core/, api/, mcp/, tools/, and tests/.
No proxy files remain in navi/tools/ root.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>