Replace -beta sidecar and .OLD backup with DB snapshots

Beta deploys used to rename foo.gsc -> foo.OLD and write beta bytes to
a foo-beta.gsc sidecar, forcing the mod loader to know the naming
convention. Now the beta content lives at the actual target filename
(same as configs already did) and the pre-beta bytes are captured in
a new beta_file_snapshots table for rollback.

- schema.sql: new beta_file_snapshots(beta_id, server, rel_path,
  prior_content BLOB, prior_sha256, prior_size). Handles scripts,
  plugins, and the composed dedicated_sp.cfg uniformly.
- db/index.ts: assertSnapshotSchemeSafe boot guard refuses to start
  if a legacy running/ready-promote beta is present on first upgrade.
  A settings sentinel (snapshots_v1) makes it one-shot.
- beta.ts openBeta: read prior bytes, insert snapshot, overwrite
  target directly.
- beta.ts rollbackBeta: restore from snapshot if had_original, else
  delete the fresh file. Drop snapshot rows after restore.
- beta.ts promoteBeta: no more rm -beta / rm .OLD calls, pull prior
  content from the snapshot table for the deployment audit, drop
  snapshots after promote.
- files.ts: delete betaFile() and oldFile().
- drift.ts: docstring updated; no special-casing needed since beta
  bytes and inventory now agree on the target rel_path.
- servers/[name]/+page.svelte: drop dead -beta/.OLD row filters.
- tests: plugin write asserts the target filename; unused
  betaFile/oldFile tests removed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/routes/servers/[name]/+page.svelte

@@ -466,13 +466,13 @@
     </section>
 
     <section class="panel">
-        <h2>Scripts on this server ({inventory.filter((f) => !f.relPath.endsWith('.OLD') && !/-beta\./.test(f.relPath)).length})</h2>
+        <h2>Scripts on this server ({inventory.length})</h2>
         {#if inventory.length === 0}
             <p class="empty">no scripts tracked — upload one from the Scripts page and open a beta to deploy it here</p>
         {:else}
             <div class="inv-list">
                 {#each inventory as f (f.relPath)}
-                    <div class="inv-row inv-{f.relPath.endsWith('.OLD') ? 'old' : /-beta\./.test(f.relPath) ? 'beta' : 'live'}">
+                    <div class="inv-row">
                         <span class="rel mono">{f.relPath}</span>
                         <span class="size mono">{f.size}B</span>
                         <span class="src mono">{f.source ?? '—'}</span>
@@ -910,9 +910,7 @@
         font-size: var(--text-mono-sm);
         align-items: center;
     }
-    .inv-row.inv-old { opacity: 0.55; border-left: 3px solid var(--ink-500); }
-    .inv-row.inv-beta { border-left: 3px solid var(--amber-500); }
-    .inv-row.inv-live { border-left: 3px solid var(--spark-500); }
+    .inv-row { border-left: 3px solid var(--spark-500); }
     .inv-row .rel { color: var(--cream); word-break: break-all; }
     .inv-row .size, .inv-row .src, .inv-row .sha { color: var(--ink-500); }
 </style>