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that only ever matched a superseded default, and real edits are left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/Program.cs

@@ -63,6 +63,7 @@ builder.Services.AddSingleton<AttachmentStore>();
 builder.Services.AddHostedService<StaleTaskRecovery>();
 builder.Services.AddHostedService<OrphanRecovery>();
 builder.Services.AddHostedService<AttachmentOrphanRecovery>();
+builder.Services.AddHostedService<PromptFileRecovery>();
 builder.Services.AddSignalR().AddJsonProtocol(options =>
 {
     options.PayloadSerializerOptions.Converters.Add(new System.Text.Json.Serialization.JsonStringEnumConverter());