Expire trash after 30 days, and make the deadline something you can see

Trash had no end. A note sat in /trash until someone emptied it by hand, and
its attachment BYTES sat on disk the whole time — the pile-up the operator
asked about. Nothing purged; there was no scheduler at all.

Retention is server-owned: `trash_retention_days` (default 30, 0 = keep
forever) in the settings registry, so it lands in admin Settings with no
migration and takes effect without a restart. A background sweep started in
before_serving does the work. Clients learn about a purge the way they learn
about any deletion — as a tombstone on the delta feed.

An auto-purge nobody can see coming is data loss on a timer, so the window is
now visible: /api/config publishes it, notes carry `deleted_at`, Trash leads
with the policy, and each card counts down. The countdown rounds DOWN — saying
"1 day left" for a note with ten minutes on the clock is the one error here
that actually costs someone a note.

Three things this turned up on the way:

- `DELETE /api/notes/<id>` hard-deleted the row, leaving no tombstone at all.
  A permanent delete in the web UI never reached a linked device, which would
  keep its copy forever and push it back on the next edit. It now purges
  through the same path as everything else.
- The purge left `note_revisions` and `note_link_previews` behind. A revision
  holds the full body, so the text of a "permanently deleted" note was still
  sitting in the database.
- `deleted_at` now SURVIVES a purge instead of being cleared. It's still true,
  and it means every query that says "not trashed" excludes tombstones for
  free — without it a content-less row reads as a perfectly normal active note
  and shows up on the board as a blank card.

Desktop keeps its own clock only when there's nobody else to keep one: the
sweep runs at startup on an UNLINKED device and refuses otherwise. A linked
client that expired notes on its own schedule could destroy something the
server was deliberately keeping, then push that delete upstream. Local policy
must never outrank the server's — so it also adopts the server's window for
the countdown rather than showing its offline default.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SreJkbxB4gx8pPsu8QbLPi

frontend/src/stores/config.ts

@@ -7,6 +7,8 @@ export interface PublicConfig {
   allow_registration: boolean;
   version: string;
   enable_url_unfurl: boolean;
+  // How many days a note survives in Trash before the server purges it. 0 = forever.
+  trash_retention_days: number;
 }
 
 // Public, unauthenticated app config (site name, whether signups are open).
@@ -15,6 +17,10 @@ export const useConfigStore = defineStore("config", () => {
   const allowRegistration = ref(true);
   const version = ref("");
   const enableUrlUnfurl = ref(true);
+  // Mirrors the server default (settings.REGISTRY). Only used if /api/config is
+  // unreachable — and 30 is a safer stand-in than 0, since claiming "kept forever"
+  // when the server is actually purging is the wrong way to be wrong.
+  const trashRetentionDays = ref(30);
   const loaded = ref(false);
 
   async function load(): Promise<void> {
@@ -25,6 +31,7 @@ export const useConfigStore = defineStore("config", () => {
       allowRegistration.value = cfg.allow_registration;
       version.value = cfg.version;
       enableUrlUnfurl.value = cfg.enable_url_unfurl ?? true;
+      trashRetentionDays.value = cfg.trash_retention_days ?? 30;
     } catch {
       // Keep defaults if the config endpoint is unreachable.
     } finally {
@@ -37,5 +44,5 @@ export const useConfigStore = defineStore("config", () => {
     await load();
   }
 
-  return { siteName, allowRegistration, version, enableUrlUnfurl, loaded, load, reload };
+  return { siteName, allowRegistration, version, enableUrlUnfurl, trashRetentionDays, loaded, load, reload };
 });