fix(publish): prune stored runtime assets of superseded page versions

[ngocht]

Summary

Every full publish stores each page's bundled runtime files in published_runtime_assets under a fresh version path, and nothing ever deleted them. On a busy production site the table reached 206k rows / 1.5 GB of a 2 GB database. One day of editing wrote 696 MB (about 19 files / 310 KB per page version). These bytes are only a fallback behind the disk-baked copies (tryServeRuntimeAsset is disk-first), but they bloat the database and every backup.

Change: persistSitePublish now deletes, per page, the stored assets of every version other than the one being activated and the one it supersedes.

• Nothing re-activates an old version: active_version_id is only ever set to the version being published.
• Keeping the superseded version covers visitors still holding its HTML. That's the same window the disk's two-slot swap covers.
• Version rows (and site_snapshots) are untouched.
• The first publish after upgrading drops the backlog for the published pages, so that one publish does a larger delete. Operators reclaim the disk space with VACUUM FULL published_runtime_assets (Postgres) or VACUUM (SQLite).

Not in scope: site_snapshots also grow by one full site document per publish. Pruning them needs a version-history retention decision.

Verification

• bun run build — ran tsc -p tsconfig.app.json and tsc -p tsconfig.node.json (clean)
• bun test — ran bun test src/__tests__/server/: 1115 pass. New publishRuntimeAssetRetention.test.ts (real SQLite via createTestDb): after four publishes only the last two versions per page keep assets and all version rows remain; fails on main. The cmsPublish fake DB handles the two new queries.
• bun run lint — eslint on the changed files (clean)
• Docker/deployment check, if relevant

Checklist

• Tests cover behavior changes.
• Docs were updated when behavior, config, deployment, or public surfaces changed.
• No compatibility shim was added for old pre-release behavior.
• No secrets, local databases, uploads, or generated artifacts are included.

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