feat(audit): /logs page — view + download recent audit log files

Adds a Streamlit page at ``/logs`` listing every
``datatools-*.jsonl`` file in ``audit_log_dir()`` (7-day window
per the retention sweep in b3ae913). Each entry shows filename,
mtime, byte size, and a ``st.download_button``. Today's file
gets its own section at the top.

The page also surfaces both paths as copyable monospace text:
the active log path (so users can grep/cat it directly on their
machine) and the folder path (so they can paste into Explorer /
Finder).

Wired into navigation via ``st.Page("pages/_Logs.py", ...)`` with
``url_path="logs"``. The sidebar entry is hidden by the same
``hide_streamlit_chrome`` CSS rule that hides ``/activate`` and
``/close`` — same pattern, same ``:has()`` + plain-fallback
selectors so the LinkContainer collapses cleanly in modern
browsers and the anchor is at least un-clickable in older ones.

License gate is OFF for this page (``gate_license=False``) — if a
user's license expires they may need logs to file a support
request; locking them out of their own audit history would be
hostile.

Next commit will wire the popover link.

Rollback: ``git revert HEAD`` removes the page and its nav entry;
the audit log itself keeps working.

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

src/gui/app.py

@@ -116,6 +116,12 @@ def _build_navigation() -> dict[str, list]:
         icon=":material/key:",
         url_path="activate",
     )
+    logs = st.Page(
+        "pages/_Logs.py",
+        title="Logs",
+        icon=":material/description:",
+        url_path="logs",
+    )
     close = st.Page(
         "pages/99_Close.py",
         title=_t("nav.close_title") or "Close",
@@ -129,7 +135,7 @@ def _build_navigation() -> dict[str, list]:
     # ``href``, leaving Home visible and no orphan section header /
     # drilldown marker in the sidebar.
     return {
-        "": [home, activate, close],
+        "": [home, activate, logs, close],
         section_label("cleaners"): by_section["cleaners"],
         section_label("transformations"): by_section["transformations"],
         section_label("automations"): by_section["automations"],