Tech debt cleanup: fix session.py, remove stale references, update docs

- db/session.py: fix indentation (2→4 space), pool_size=0 (unlimited),
  remove "ned to look at this" typo
- Remove glue.models from alembic env.py import list
- Update shared __init__.py, menu_item.py docstring, calendar_impl.py,
  handlers/__init__.py to remove glue terminology
- Remove federation_handlers.py tombstone file
- Remove TODO comments (replace with explanatory comments)
- Rewrite README.md to reflect current architecture
- Update anchoring.py TODO to plain comment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

events/handlers/__init__.py

@@ -1,4 +1,4 @@
-"""Shared event handlers (replaces glue.setup.register_glue_handlers)."""
+"""Shared event handlers."""
 
 
 def register_shared_handlers():
@@ -6,5 +6,4 @@ def register_shared_handlers():
     import shared.events.handlers.container_handlers  # noqa: F401
     import shared.events.handlers.login_handlers  # noqa: F401
     import shared.events.handlers.order_handlers  # noqa: F401
-    # federation_handlers removed — publication is now inline at write sites
     import shared.events.handlers.ap_delivery_handler  # noqa: F401

events/handlers/federation_handlers.py

@@ -1,8 +0,0 @@
-"""Federation event handlers — REMOVED.
-
-Federation publication is now inline at the write site (ghost_sync, entries,
-market routes) via shared.services.federation_publish.try_publish().
-
-AP delivery (federation.activity_created → inbox POST) remains async via
-ap_delivery_handler.
-"""