chore(release): bump to v0.7.20 + changelog

[argszero]

Summary

Release v0.7.20 — host-authorized release (rant 2026-08-25T12:12:53: "aitokenpool可以发布新版本了").

Contains 1 PR since v0.7.19 (7a259bf):

1. fix(perf): warm NFS sqlite with 64MB cache + transactions indexes + parallel trend (rant 2026-08-25T12:02:13) #150 (8aa8493) fix(perf): warm NFS sqlite with 64MB cache + transactions indexes + parallel trend (rant 2026-08-25T12:02:13 — slow transactions page on NFS-backed dev DB):
   • db.rs open(): PRAGMA cache_size=-65536 + mmap_size=67108864 — whole DB resident in process memory, NFS read once (measured 2.39s → 0.40s per COUNT)
   • v12 migration: 4 indexes on transactions (user_id, user_id+id DESC, user_id+time, user_id+type)
   • Frontend: loadTransactions fetches list + trend via Promise.all (saves one ~0.9s serial hop)

Changes

• Cargo.toml / Cargo.lock: 0.7.19 → 0.7.20
• ui/index.html: cache-bust 20260825-4 → 20260825-5
• CHANGELOG.md: v0.7.20 entry

Tests

• cargo test — 148/148 pass
• cargo fmt --check clean
• cargo clippy clean
• node --check ui/js/app.js OK

Deploy notes

• No WAL (unsupported on network filesystems), DB stays on NAS (deployment hard constraint).
• After merge: tag v0.7.20 on main tip → Docker Publish → deploy repo ci/docker-compose.yml image bump → GitLab pipeline → dev auto-deploy.