feat(career): hours-per-genre odometer — honest wall-clock play time (#942)

Career v2, WS2. Nothing measured play time before (the achievements
plugin's final-position shortcut double-counts loops and mis-reads
seeks). Now:

- stats-recorder.js accrues WALL-CLOCK seconds across song:play/resume ↔
  pause/stop/ended spans (single spans clamp at 2h against suspend
  inflation) and piggybacks them as `seconds` on the POSTs it already
  sends; failed POSTs restore the accumulator; a session reset flushes
  first so time can't re-attribute to the next song/arrangement.
- POST /api/stats accepts optional `seconds` (finite, 0 < s ≤ 6h) on the
  scored and position branches, plus a new seconds-only branch for
  unscored plays that ran to the natural end — banks time WITHOUT
  touching the resume position (song:ended must not overwrite Continue)
  and still counts as playing today for the streak.
- song_stats gains additive idempotent `seconds_total`; record_session/
  touch_position accrue, new add_play_seconds() for the seconds-only
  path; the legacy-encoding stats merge sums seconds across duplicates.
- Passports surface it: "14.2 h in Blues" under the badge stamp and on
  the shelf cover sub-line — a true fact that only grows, never a
  target or a meter (Stage 5 post-cap, per the career design).

Tests: seconds accrual/validation/seconds-only branch (stats API),
per-instrument-and-genre summing (career), fmtHours formatting (vm).
Full suites: pytest 2480, JS 1165.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

tests/plugins/career/conftest.py

@@ -26,7 +26,8 @@ class FakeMetaDb:
         self.conn.execute(
             """CREATE TABLE song_stats (
                    filename TEXT, arrangement TEXT, best_accuracy REAL,
-                   last_played_at TEXT
+                   last_played_at TEXT,
+                   seconds_total REAL NOT NULL DEFAULT 0
                )"""
         )
         self.conn.execute(
@@ -37,9 +38,10 @@ class FakeMetaDb:
         )
 
     def add(self, filename, arrangement, best_accuracy, in_library=True,
-            genre="", arrangements=None, last_played_at=None):
-        self.conn.execute("INSERT INTO song_stats VALUES (?, ?, ?, ?)",
-                          (filename, arrangement, best_accuracy, last_played_at))
+            genre="", arrangements=None, last_played_at=None, seconds_total=0):
+        self.conn.execute("INSERT INTO song_stats VALUES (?, ?, ?, ?, ?)",
+                          (filename, arrangement, best_accuracy, last_played_at,
+                           seconds_total))
         if in_library:
             self.conn.execute(
                 "INSERT INTO songs SELECT ?, ?, ?, ?, ? WHERE NOT EXISTS "