feat(core): re-run a published version's migration when its revision is bumped

[dr-bonez]

Why

Every master push republishes Current to alpha under the same version number, but pre_init only migrates a db whose recorded version is behind Current. A server that has committed a version keeps that version's up() as it was on the day it updated. 0.4.0.2's migration has changed three times since alpha boxes first took it — the ALPN rewrap (#3777), the server-name drop and hostname repair (#3791) — and none of that has run on them.

What

• VersionT gains migration_revision() (default 0). commit records the revision it applied in serverInfo.latestMigrationRevision.
• pre_init's Ordering::Equal branch re-runs up() + commit() when the stored revision differs from the running binary's. commit re-queues the version in postInitMigrationTodos, so post_up() runs again too.
• A db without the field reads as revision 0 (#[serde(default)]); Public::init seeds a fresh install at Current's revision so it never migrates itself on first boot.
• 0.4.0.2 is bumped to revision 1 so every server already on it applies the steps it missed, once. Its up() was already idempotent (the ALPN, port-80, name and hostname steps each no-op on an already-migrated db).
• Docs: the trait doc and VERSION_BUMP.md state the contract — bumping a revision requires the migration to be idempotent with its previous revision, since the re-run happens on a db the earlier up() already transformed, never on the pre-migration shape.
• Regenerated ServerInfo.ts; the UI mock carries the new field.

No changelog entry: 0.4.0.2 is untagged, and the only user-visible effect is that alpha/beta servers receive fixes already listed under it.

Verification

• cargo test -p start-core --features=test version:: — 31 passed, including two new tests (a_db_that_predates_revisions_reads_as_revision_zero, commit_records_the_revision_of_the_migration_it_applied)
• bindings regenerated with CI's feature set (test,dev,unstable); only ServerInfo.ts changed
• npm run build:core && npm run check:ui && npm run check:setup clean
• pinned rustfmt + prettier clean