v0.4.0: live feed updates (auto-insert new posts)

New artifacts appear at the top of the feed without a manual refresh.

- GET /feed/updates (session-authed): new artifacts since a timestamp marker,
  owner-scoped and filter-aware (source/label/kind/q), returned as row HTML.
- Feed JS polls every 5s, paused while the tab is hidden (immediate poll on
  refocus). Prepends new rows into today's group without touching the selected
  row or the preview iframe — what you're reading stays put and selected.
- Fresh rows show "now", aging into their real time after ~3 min; brief
  highlight on arrival.
- Extracted _artifact_rows.html partial, shared by the day-group render and the
  updates endpoint, so live rows match exactly.
- Polling chosen over SSE/WebSockets: zero infra on sync-WSGI + SQLite (see
  planning/next_steps for the SSE upgrade path). 142 tests pass; feed page +
  endpoint verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -9,6 +9,23 @@ former name, "Daybook".)
 
 _Nothing yet._
 
+## [0.4.0] — 2026-09-04
+
+### Added
+- **Live feed updates.** New artifacts now appear at the top of the feed
+  automatically, without a manual refresh — the browser polls a lightweight
+  `GET /feed/updates` every 5s (paused while the tab is hidden, one immediate
+  poll on refocus). Owner-scoped and **respects the active source/label/kind/q
+  filters**, so a new post that doesn't match your current view won't show. The
+  currently selected/previewed artifact stays put and visibly selected. Fresh
+  rows display "now" and age into their real time after a few minutes.
+  (Chosen over SSE/WebSockets deliberately: zero new infrastructure on the
+  sync-WSGI + SQLite stack; see `planning/next_steps/` for the SSE upgrade path.)
+
+### Changed
+- Extracted the feed row markup into a reusable `_artifact_rows.html` partial
+  (shared by the day-group render and the live-updates endpoint).
+
 ## [0.3.2] — 2026-09-04
 
 ### Added
@@ -138,7 +155,8 @@ First tagged release.
 - Dockerised (Gunicorn + whitenoise), SQLite, `git`-based deploy with a
   runbook (`deploy/cloud_agent_deploy.md`) and health check.
 
-[Unreleased]: https://git.cygnus.systems/peter/daybook/compare/v0.3.2...HEAD
+[Unreleased]: https://git.cygnus.systems/peter/daybook/compare/v0.4.0...HEAD
+[0.4.0]: https://git.cygnus.systems/peter/daybook/compare/v0.3.2...v0.4.0
 [0.3.2]: https://git.cygnus.systems/peter/daybook/compare/v0.3.1...v0.3.2
 [0.3.1]: https://git.cygnus.systems/peter/daybook/compare/v0.3.0...v0.3.1
 [0.3.0]: https://git.cygnus.systems/peter/daybook/compare/v0.2.1...v0.3.0