feat(filters+ui): per-element author/publisher filters, playlist toggles, Up Next API, reorder UI, dashboard badges

Phases 4 + 5 of the metadata overhaul (plan §4, §5) plus §3 handler
wiring.

Filters (§4.1): author_filter/publisher_filter now match per-element
against the authors[]/publishers[] arrays — a co-authored book matches
any one of its authors — with comma-joined params acting as
OR-within-facet multi-select (string_to_array + cross unnest). Legacy
single-value params unchanged on the wire; series/genre/language
filters stay on their varchar columns; narrator filter already
per-element.

Collections API (§3.3-3.5): collection detail carries viewer +
hide_finished into the listing query and exposes up_next (visible-
library-enforced reading-queue head); PUT
/api/collections/:id/items/order (owner-only, full-order rewrite);
UpdateCollectionRequest gains hide_finished/show_up_next ([]
string last-value-wins for the hidden-false-sibling checkbox pattern)
merged server-side OVER stored view_settings so imported_from_series
provenance survives edits; EditCollectionModal renders the toggles
from view_settings.

Dashboard (§5.5): sections JSON carries is_playlist/complete
(dashboard.ts is the AGENTS-documented JSON-render exception; first
paint stays templ). Fully-read playlists render '✓ Playlist complete'
instead of an empty rail; imported playlists get a 📖 Playlist badge.

Frontend: book detail shows subtitle + full authors + Explicit badge;
edit modal gains subtitle, comma-separated authors/publishers (client-
split to arrays exactly like narrators), step=any series number,
explicit checkbox; collection book cards get playlist move ↑/↓ buttons
persisting the full order via the reorder endpoint (templ partial
re-render on failure — DOM order is client-local, API order is truth).

AGENTS.md gotcha #3 amended per plan §3.7: user collections are
dashboard sections by default; the show_on_dashboard premise is
retired.

Verified: full affected integration sweep green (pins widened for
up_next/is_playlist/complete — changelog entries in
docs/contract_pins.md); unit suite green; go build + templ + vite
green.

AGENTS.md

@@ -161,14 +161,19 @@ of a server bug: stop and flag the user.
    the cache stale until the next API-path write — never "preview"
    rule changes via psql and expect them applied (2026-10-14: a live
    curl test flip looked ignored until the API path was used).
-3. **User collections are not dashboard sections**: nothing sets
-   collection show_on_dashboard for user rows, and GetDashboardSections
-   skips empty user sections. Collection detail (JSON + SSR) must NOT
-   route user rows through the dashboard-section path — a 7ce7321
-   regression did exactly that (static detail without library_id
-   returned zero books until 0a7fbd6). Only real system query types
-   (continue-reading etc.) route there; `query_type='filter'` is the
-   schema DEFAULT on every user row, not a query type.
+3. **User collections are not dashboard query types** (amended 2026-10-19,
+   A2c): user collections ARE dashboard sections by default now —
+   GetUserCollectionsForDashboard no longer gates on show_on_dashboard
+   (which remains system-section provisioning state; hiding is
+   dashboard-prefs `hidden_collections` territory). GetDashboardSections
+   still skips genuinely empty user sections, but hide_finished
+   collections emit a Complete section instead of vanishing. Collection
+   detail (JSON + SSR) must still NOT route user rows through the
+   dashboard-section path — a 7ce7321 regression did exactly that
+   (static detail without library_id returned zero books until 0a7fbd6).
+   Only real system query types (continue-reading etc.) route there;
+   `query_type='filter'` is the schema DEFAULT on every user row, not a
+   query type.
 4. **End-of-day arithmetic**: anchor the END bound to the START of the
    day, never to NOW(). `now.AddDate(0,0,1) − 1ns` carries this
    instant's clock time into tomorrow — a range "ending today"