perf: runtime performance pass, phase 1 (DB pragmas, batched scan writes)

Executes docs/superpowers/specs/2026-07-07-runtime-performance-pass-design.md:

- database.rs: every pooled connection now runs WAL + synchronous=NORMAL
  + busy_timeout=5000 + foreign_keys=ON via with_init (in-memory pools
  get the latter two). Fixes the SQLITE_BUSY failure mode under the
  parallel scanner and makes FK cascades work on every connection, not
  just whichever one last ran the old one-shot pragma in delete_folder.
- database.rs: prepare_cached for the per-video info_cache queries; new
  info_cache_put_many bulk upsert (single transaction) replaces the
  per-row autocommitted info_cache_put, with a round-trip unit test.
- library.rs: enrich_with_cache collects cache misses and flushes them
  once per channel; title sort uses sort_by_cached_key.
- app.rs: Title/ChannelAsc sorts use sort_by_cached_key instead of
  allocating two lowercased strings per comparison.
- Cargo.toml: panic=abort in release (crash-hook still fires; Cargo
  forces unwind for test harnesses). PACKAGING.md documents the local
  RUSTFLAGS target-cpu=native opt-in; repo stays portable.
- .gitignore: catacomb.db-wal / catacomb.db-shm sidecars.

Verified: 146 tests pass (integration suite exercises the pragmas
end-to-end), x86_64-pc-windows-gnu check green, live smoke shows
journal_mode=wal + batched cache writes landing correct rows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/library.rs

@@ -449,6 +449,10 @@ fn collect_raw_videos(entries: impl Iterator<Item = std::fs::DirEntry>) -> Vec<R
 }
 
 fn enrich_with_cache(raws: Vec<RawVideo>, cache: Option<&Database>) -> Vec<Video> {
+    // Cache misses are collected here and flushed in ONE transaction after
+    // the loop (`info_cache_put_many`). On a cold cache every video is a
+    // miss, so per-row autocommitted upserts would pay one commit per video.
+    let mut cache_misses: Vec<(String, u64, Option<f64>, bool, Option<String>)> = Vec::new();
     let mut videos: Vec<Video> = raws.into_iter().map(|raw| {
         // Parse info.json once for both duration and chapter presence.
         // The cache (if provided) lets us skip the read+JSON parse when
@@ -485,8 +489,8 @@ fn enrich_with_cache(raws: Vec<RawVideo>, cache: Option<&Database>) -> Vec<Video
                         (dur, chap, date)
                     })
                     .unwrap_or((None, false, None));
-                if let (Some(mt), Some(db)) = (mtime, cache) {
-                    db.info_cache_put(&path_str, mt, parsed.0, parsed.1, parsed.2.as_deref());
+                if let (Some(mt), Some(_)) = (mtime, cache) {
+                    cache_misses.push((path_str.into_owned(), mt, parsed.0, parsed.1, parsed.2.clone()));
                 }
                 parsed
             })
@@ -516,7 +520,11 @@ fn enrich_with_cache(raws: Vec<RawVideo>, cache: Option<&Database>) -> Vec<Video
             upload_date,
         }
     }).collect();
-    videos.sort_by_key(|v| v.title.to_lowercase());
+    if let Some(db) = cache {
+        db.info_cache_put_many(&cache_misses);
+    }
+    // sort_by_cached_key: lowercase each title once, not once per comparison.
+    videos.sort_by_cached_key(|v| v.title.to_lowercase());
     videos
 }