feat(booth): pin/favorite, multi-select delete, newest-first link board

The standing link board grew from a flat oldest-first list with a per-row
× into a manageable board: newest links lead, favorites stay on top, and
several dead links can go in one pass.

- Ordering: order_for_display() renders pinned rows first, then newest-first
  within each group (the board is an append log, so newest = most recently
  posted — the row you usually came to grab).
- Pin/favorite: a per-row ★ toggles pinned state via POST /b/<name>/pin.
  State lives in a .pins sidecar dotfile (one content id per line), NOT
  inline in links.md — so links.md stays a pure atomic-append log (many
  sessions post concurrently) and a row's content id never changes just
  because it was pinned. remove_link_entry drops a removed row's pin;
  orphaned pins are inert (renderer only stars a live id).
- Multi-select delete: checkboxes feed POST /b/<name>/unlink-many (repeated
  'sel' content ids), with a select-all box and a live count. The per-row ×
  stays for single removal.
- One <form> with formaction buttons, so checkboxes, ×, ★, and bulk delete
  coexist without nested forms AND all work with JS off; JS only adds
  select-all and the live count. Per-row × confirm reads desc/url from
  data-* attrs, so an arbitrary posted description can't break into the JS.
- Every action is keyed by content id, never row position — same race-safety
  the existing × has, extended to the bulk path.
- Fixed pre-existing undefined --fg/--bg CSS refs in the board styles.

Tests: +19 (pins round-trip, ordering, orphan-inert, remove-unpins, /pin
and /unlink-many endpoints, board render + order). Full suite 102 passing.
Deployed to nh3-dev booth.service; verified live (newest-first, pin
round-trip, bulk delete) against the real 31-row board with no data loss.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "booth"
-version = "0.1.7"
+version = "0.1.8"
 description = "The Booth — a dead-simple standing web server that scans a data dir of drop-folders and renders each as an ephemeral media 'booth' (image/webm/audio auto-gallery, or a folder's own index.html verbatim). Also accepts browser/curl uploads for pickup under a human-readable id. 24h TTL, then the folder is wiped. Fleet tool for CC sessions to surface A/B and smoke results to the operator."
 requires-python = ">=3.11"
 dependencies = [