fix(prompts): stop on-disk prompt overrides from freezing forever

EnsureExists blindly seeded ~/.todo-app/prompts/*.md with the bundled
default and never revisited it, so any file created by opening the
Files settings tab shadowed every later default change permanently
(SuggestImprovement/AskUser sections never reached real runs since
2026-06-04). PromptFiles now hashes what a file was seeded/saved with
in prompts/.defaults.json: Classify() tells missing/current-default/
known-past-default/edited apart, ReconcileStaleDefaults() drops files
that only ever matched a superseded default, and real edits are left
alone and surfaced in the Files tab with a diff + reset-to-default
action. QuarantineOrphans() moves stale-named leftovers (agent.md,
planning.md) into prompts/_orphans instead of silently deleting them.
Wired as a Worker startup sweep (PromptFileRecovery) alongside the
existing OrphanRecovery/AttachmentOrphanRecovery services.

src/ClaudeDo.Worker/Lifecycle/PromptFileRecovery.cs

@@ -0,0 +1,36 @@
+using ClaudeDo.Data;
+
+namespace ClaudeDo.Worker.Lifecycle;
+
+/// <summary>
+/// Startup-only sweep: drops any prompt override file that only matched a now-superseded
+/// bundled default and was never actually edited (see <see cref="PromptFiles.ReconcileStaleDefaults"/>),
+/// and quarantines any *.md file under the prompts root that no longer maps to a known
+/// <see cref="PromptKind"/> (leftovers from a retired naming scheme).
+/// </summary>
+public sealed class PromptFileRecovery : IHostedService
+{
+    private readonly ILogger<PromptFileRecovery> _logger;
+    private readonly string? _root;
+
+    public PromptFileRecovery(ILogger<PromptFileRecovery> logger, string? root = null)
+    {
+        _logger = logger;
+        _root = root;
+    }
+
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        PromptFiles.ReconcileStaleDefaults(_root);
+
+        var orphans = PromptFiles.QuarantineOrphans(_root);
+        if (orphans.Count > 0)
+            _logger.LogWarning("Prompt file recovery: quarantined {Count} orphaned prompt file(s) into _orphans", orphans.Count);
+        else
+            _logger.LogInformation("Prompt file recovery: no orphaned prompt files found");
+
+        return Task.CompletedTask;
+    }
+
+    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+}