feat(tuning): weekly trend view — per-surface series + knob-turn markers

The verify half of the tune→verify loop (#1251), on the same admin
Tuning page as the knobs:

- RecommendationWeeklyTrends: weekly per-source outcomes aggregated
  across all users (the knobs are global, so judging a turn needs
  global outcomes — rows carry rates only, no track/user identity),
  with a taste-hit count per bucket: plays whose track's artist has a
  positive weight in the player's current taste profile. That's the
  "cheap recompute" reading — retroactive over the whole window, at
  the cost of profile drift.
- GET /api/admin/recommendation-trends?weeks=N (default 12, cap 52):
  per-family weekly series (skip rate, sample-weighted completion,
  taste-hit rate) plus the tuning-audit markers inside the window.
- Web: sparkline table under the tuning cards — skip rate per week on
  a shared axis with dashed ticks at knob turns, latest-week columns,
  window taste-hit rate, low-volume rows dimmed as anecdote, and a
  plain-text list of the window's tuning changes.

Also fixes the revive unused-parameter lint on the tuning GET handler
that failed CI run 1903 on the previous commit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TsF3cNoKrqCYsU78cXC8U6

internal/db/queries/recommendation_metrics.sql

@@ -8,6 +8,37 @@
 -- the Go handler; completion_n is carried so family merges can weight
 -- avg_completion correctly.
 
+-- name: RecommendationWeeklyTrends :many
+-- Weekly per-source outcome series for the tuning lab's trend view
+-- (#1251). Aggregated across ALL users: the tuning knobs are global,
+-- so judging a knob turn needs global outcomes — rows carry rates
+-- only, no track or user identity. NULL-source (manual) rows are
+-- included as the baseline family.
+--
+-- taste_hits counts plays whose track's artist has a positive weight
+-- in that user's CURRENT taste profile — the "cheap recompute" option:
+-- retroactive over the whole window, at the cost of drift (the profile
+-- is today's, the play may be weeks old). Good enough to read whether
+-- a surface is feeding taste-fitting tracks.
+-- $1 window in weeks.
+SELECT
+    date_trunc('week', pe.started_at)::date AS week_start,
+    pe.source,
+    count(*)::bigint AS plays,
+    count(*) FILTER (WHERE pe.was_skipped)::bigint AS skips,
+    count(pe.completion_ratio)::bigint AS completion_n,
+    COALESCE(avg(pe.completion_ratio), 0)::float8 AS avg_completion,
+    count(*) FILTER (WHERE tpa.artist_id IS NOT NULL)::bigint AS taste_hits
+FROM play_events pe
+JOIN tracks t ON t.id = pe.track_id
+LEFT JOIN taste_profile_artists tpa
+       ON tpa.user_id = pe.user_id
+      AND tpa.artist_id = t.artist_id
+      AND tpa.weight > 0
+WHERE pe.started_at > now() - (sqlc.arg(weeks)::int * INTERVAL '1 week')
+GROUP BY 1, 2
+ORDER BY 1, 2;
+
 -- name: RecommendationSourceMetricsForUser :many
 -- $1 user_id, $2 window_days. plays/skips are counts; avg_completion is the
 -- mean completion ratio over the completion_n plays that recorded one.