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>

Cargo.toml

@@ -75,6 +75,14 @@ codegen-units = 1
 # runtime; those are less informative without symbols but usable with
 # addr2line against the unstripped build artifact.
 strip = "debuginfo"
+# No unwinding tables/landing pads: smaller binary, marginally faster hot
+# paths. The crash handler (crash.rs panic hook) still fires before the
+# abort, so crash logging is preserved. Cargo forces `panic=unwind` for
+# test/bench harnesses automatically, so `cargo test --release` and the
+# #[cfg(test)] catch_unwind in crash.rs are unaffected. Tradeoff: a panic
+# in a parallel scan worker aborts the process instead of one worker —
+# acceptable, those workers treat all fallible I/O with .ok() already.
+panic = "abort"
 
 # ── Debian / Ubuntu package (cargo-deb) ──────────────────────────────────────
 # `cargo deb` reads this to build a .deb. Runtime deps mirror the PKGBUILD: