Add lyrics: paste, fetch, and read them while reviewing

Lyrics are suggested at submission and never imposed. The conversion worker
makes one LRCLIB lookup with whatever metadata exists, and the waiting page
has a Hae sanoitukset button that re-queries with whatever title and artist
are currently typed — which is the case that matters, since our metadata comes
from ID3 tags and YouTube uploaders. Neither path overwrites typed text.

- lyrics text on both submissions and songs, copied across at publish. Nothing
  has launched, so the column goes into 001_init.sql rather than a migration
- The lock does not cover lyrics: it freezes what the song claims to be, and
  nobody reviewed the lyrics. So the submitter can still fix them afterwards,
  or paste them for an old song a year later
- The review strip gained a second pane: lyrics on the left, review on the
  right, so following the words costs no scrolling. No lyrics means no pane,
  not an empty one. Below 1024px the panes stack
- LRC timestamps are stored but stripped for reading — they belong to the
  player, not the reader
- The lyrics box is capped and scrolls inside itself, so a long song cannot
  stretch the strip past the screen

Fixes a real bug found on the way: saveMetadata cleared any field the request
did not carry, so publishing wiped the lyrics the worker had just fetched.
Fields absent from a request now keep their stored value.

The client identifies itself to LRCLIB as "levyraati" and nothing more.

Tests cover cleanLyrics keeping line breaks, and fetchLyrics against a local
server: synced beats plain, instrumentals and wrong-length takes are skipped,
and a miss is empty with no error.

docs/decisions.md

@@ -191,3 +191,21 @@ says so.
     starting at 1, for the second attempt at a release. The string lives in a git tag and reaches
     the binary through `-ldflags`, so no file in the repo has to be bumped and a local build
     honestly reports `dev`. It surfaces in the footer, the startup log and `/healthz`.
+45. **Lyrics are suggested at submission, and stay editable forever.** Four decisions in one, taken
+    2026-07-31 while scoping the feature in [later.md](./later.md):
+    - **Suggested, never imposed.** The worker attempts one LRCLIB lookup after conversion, and the
+      waiting page carries a *Hae sanoitukset* button that re-queries with whatever title and artist
+      are currently typed. The button exists because our metadata comes from ID3 tags and YouTube
+      uploaders, so the automatic attempt misses exactly the songs with messy names — and would look
+      broken rather than absent. Neither path overwrites text the submitter has typed.
+    - **Lyrics live on the submission, not just the song**, and are copied across at publish, because
+      they are part of preparing a song rather than something bolted on afterwards.
+    - **No migration 002.** Nothing has launched, so the column goes into `001_init.sql` and the
+      database is recreated. The schema has no legacy to respect until there is data worth keeping.
+    - **The lock does not cover lyrics.** It exists so the thing people reviewed stops changing under
+      them, and nobody reviewed the lyrics — the rule is now *the lock freezes what the song claims
+      to be; lyrics are an attachment to it.* This also allows pasting lyrics for an old song, which
+      is when the feature is worth most.
+
+    The coverage assumption that shaped the earlier sketch was wrong and is corrected in `later.md`:
+    LRCLIB has synced lyrics for a good share of Finnish rock, not almost none.