revert: restore audit-log kill switch — async redesign didn't help

User pulled d9e32e5 (async-writer audit log + re-enabled diagnostics
sidebar) and still sees blank pages. The synchronous-write theory
from the previous round was at most a partial explanation; something
ELSE in the audit-log code path is also taking the page render down
on the user's machine.

Restore the kill switch so the user has a working app while we
diagnose:

- ``src/audit.py``: ``_DISABLED = True`` re-introduced at module
  top, each of ``log_event`` / ``log_session_start`` /
  ``log_page_open`` / ``flush_audit_log`` early-returns. The async
  writer thread is never started.
- ``hide_streamlit_chrome``: ``_render_diagnostics_sidebar()`` call
  re-gated behind ``if False:``.

The async writer code stays in place — easier to flip the flag back
when we identify the real cause than to rewrite a third time. The
shutdown-flush call in ``shutdown_app`` also stays; it early-returns
on the kill switch and is harmless.

Diagnostic plan for the next session: ask the user for the launcher
terminal output (the new stderr "DataTools audit: writes failing..."
message would tell us if the writer thread DID start and DID fail),
and whether ``~/.datatools/logs/`` is being created at all.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/gui/components/_legacy.py

@@ -158,17 +158,18 @@ def hide_streamlit_chrome(*, gate_license: bool = True) -> None:
         require_license_or_render_activation,
     )
     render_license_status_sidebar()
-    # Diagnostics sidebar re-enabled now that the audit log is async
-    # and ``audit_log_path()`` is a pure path computation (no mkdir
-    # on the request path). Still wrapped in try/except defensively;
-    # a render error here prints to stderr instead of taking down
-    # the page body.
-    try:
-        _render_diagnostics_sidebar()
-    except Exception:
-        import traceback, sys
-        print("DataTools: diagnostics sidebar render failed:", file=sys.stderr)
-        traceback.print_exc()
+    # Diagnostics sidebar is DISABLED — the async-writer redesign
+    # didn't actually fix the blank-pages symptom on the user's
+    # machine. The sidebar calls ``audit_log_path()`` which is pure
+    # now, so the failure mode must be elsewhere; keep this off
+    # while we diagnose so the user has a working GUI.
+    if False:
+        try:
+            _render_diagnostics_sidebar()
+        except Exception:
+            import traceback, sys
+            print("DataTools: diagnostics sidebar render failed:", file=sys.stderr)
+            traceback.print_exc()
     if gate_license:
         require_license_or_render_activation()