docs: fix 4 stale refs (4-thread->8, dispatch line 1341->1322, 7->11 locks)

Caught these when re-verifying the 4 commits from docs_sync_test_era_20260610.
Not in my track originally (per the prior 'no track boundary' correction),
but they're stale data and easy to fix in one commit:

- docs/Readme.md:41: '4-thread ... 7 lock-protected regions' -> '8-thread
  io_pool ... 11 lock-protected regions' (bumped 4->8 in 4a338486
  on 2026-06-06; 11 locks counted in __init__ at app_controller.py:778-1212)

- docs/reports/session_synthesis_20260608.md:121: same fix, plus a
  note that this report predates the bump

- docs/reports/workflow_markdown_audit_20260608.md:40: same fix
  (the audit report was correct AT TIME OF WRITE but is now stale)

- docs/guide_tools.md:57: 'mcp_client.py:1341' -> 'mcp_client.py:1322'
  (the dispatch function's actual line)

Left unchanged:
- docs/reports/COMPACTION_DIGEST_20260607.md:45 mentions '4 workers are
  stuck' in a specific historical context (2026-06-07 hang investigation
  pre-bump). That '4' was true at the time and is part of the historical
  record; flagging in commit message not text.

docs/reports/session_synthesis_20260608.md

@@ -118,7 +118,7 @@ The user-driven insights from these corrections:
    - Debounced change-detection at render frame (`gui_2.py:1140-1170`)
    - `_handle_reset_session` (clears 30+ fields, replaces project, preserves `active_project_path` per the 2026-06-08 regression fix)
    - `App.__getattr__`/`__setattr__` state delegation to Controller (`gui_2.py:666-675`)
-   - 4-thread access pattern with 7 lock-protected regions
+   - 8-thread io_pool with 11 lock-protected regions (bumped 4→8 in 4a338486 on 2026-06-06; this report predates the bump)
    - State persistence: in-memory vs project TOML vs config TOML
    - Hot-reload integration
    - 14 file:line refs into `gui_2.py:735-789`, `history.py`, `app_controller.py:3286-3356`