Rebase #5337 (public read-only conversation sharing) onto master

Rebased 363 commits forward (branch-point 2026-07-05). Applied the PR's code
diff cleanly across 16 files; resolved api/models.py additively (both master's
process_wakeup_pause/anchor_scene_index fields AND the PR's share_token/
share_created_at fields kept in the Session constructor, metadata list, and
to_dict). CI workflow (.github/workflows/tests.yml) intentionally NOT taken from
the stale branch — master owns it (the branch's apparent removal of Playwright/
Office steps was a PAT-workflow-scope revert; rebase restores master's CI).

Co-authored-by: MicoRobot. Concept approved by maintainer (opt-in public share,
2026-07-11). Note: 4 dynamic share tests fail identically on the original
unrebased head (pre-existing test-env Session.load fragility, not rebase-caused);
to be resolved during the security re-gate in a proper sandbox.

ARCHITECTURE.md

@@ -1307,6 +1307,8 @@ Complete list of all HTTP endpoints as of Sprint 1 (v0.3).
     /api/sessions              List of all session compact() dicts, sorted by updated_at
     /api/list                  ?session_id=X&path=. -> directory listing for session workspace
     /api/file                  ?session_id=X&path=rel -> file content (text, 200KB limit)
+    /share/<token>             Public read-only HTML shell for a sanitized shared transcript snapshot
+    /api/share/<token>         Public JSON payload for a sanitized shared transcript snapshot
     /api/chat/stream           ?stream_id=X -> SSE stream. Long-lived. Emits token/tool/
                                approval/done/error events.
     /api/chat/stream/status    ?stream_id=X -> {"active": true/false, "stream_id": X}
@@ -1327,6 +1329,8 @@ Complete list of all HTTP endpoints as of Sprint 1 (v0.3).
                                -> {"stream_id", "session_id"}. Starts agent daemon thread.
     /api/chat                  (fallback, sync) {"session_id", "message", "model"?, "workspace"?}
                                -> blocks until agent finishes. Returns full result.
+    /api/share/create          {"session_id"} -> creates or refreshes a public read-only snapshot link
+    /api/share/revoke          {"session_id"} -> revokes the current public snapshot link
     /api/approval/respond      {"session_id", "choice": once|session|always|deny}
                                -> {"ok": true, "choice": choice}