fix(tools): lower working directory and workspace into fs tool descriptions

The process cwd was nowhere in the model's context: shells start in the
inherited process cwd (spawn_group_leader passes no cwd), relative file
paths resolve against it, but nothing told the model where it was
standing — in stock Docker every shell ran in /data while user files sat
in the /workspace mount, and the model's only recourse was to probe with
pwd (#857, #833).

Lower both facts into the tool schemas, where they gate intrinsically on
tool availability (a persona without fs tools carries no note, and
coordinator envelopes are untouched):

- tools/*.json: cwd_note/workspace_note metadata templates on bash,
  read_file, write_file, edit_file, search, diff_file; bash also states
  the fresh-shell-per-call semantics (cd does not persist) and drops a
  stale reference to the removed man tool.
- tools.apply_cwd_context(): renders the notes into descriptions;
  deep-copies noted tools (the fs dicts are shared across
  TOOLS/INTERACTIVE_TOOLS/TASK_AGENT_TOOLS and aliased through
  merge_mcp_tools), passes note-less tools through by reference.
- ChatSession._apply_cwd_notes(): wraps every fresh interactive build of
  _tools AND _task_tools (construction, MCP catalog change, MCP
  disconnect) — assignment-time, so the wire tools block stays
  byte-stable for provider prompt caches. os.getcwd() is OSError-guarded
  (MCP rebuilds run on a background thread; eval tears down its
  workdir); the workspace hint drops when the dir is missing or equals
  the cwd. Task-agent sub-agents carry their own notes via _task_tools,
  independent of parent persona visibility.
- config.get_workspace_dir(): [tools] workspace_dir with
  TURNSTONE_WORKSPACE env fallback (searxng pattern), informational
  only — no chdir, no path confinement (per-workstream working-dir
  grants are a separate planned feature).
- Dockerfile: ENV TURNSTONE_WORKSPACE=/workspace so stock deployments
  surface the mount with zero operator config.
- docs/docker.md: document the /data working directory, the
  working_dir: /workspace compose override as the operator-level fix,
  and the SQLite-fallback-DB-in-cwd caveat.

Closes #857

Dockerfile

@@ -60,8 +60,12 @@ COPY docker/entrypoint.sh /usr/local/bin/entrypoint.sh
 WORKDIR /data
 RUN chown turnstone:turnstone /data
 
-# Workspace mount point — bind-mount a host directory here
+# Workspace mount point — bind-mount a host directory here.  The env var
+# surfaces the path in the model's shell/file tool descriptions
+# (config.get_workspace_dir); without it the mount is invisible to the
+# model, whose cwd is /data below.
 RUN mkdir -p /workspace && chown turnstone:turnstone /workspace
+ENV TURNSTONE_WORKSPACE=/workspace
 
 USER turnstone