Add NIP-24 published_at to useNostrPublish for replaceable/addressable events

Extend useNostrPublish with an optional `prev` property on the event
template. For replaceable and addressable kinds, the hook automatically
manages published_at:

- First publish (no prev): set published_at equal to created_at
- Update (prev provided): preserve published_at from the old event
- Old event lacks published_at: don't fabricate one
- Caller already set published_at in tags: leave it alone

Callers pass `prev` when they have the old event from fetchFreshEvent,
giving the hook everything it needs without extra network requests.
Updated all 11 call sites that publish replaceable or addressable events.
Documents the prev convention in AGENTS.md.

AGENTS.md

@@ -699,23 +699,47 @@ The `useCurrentUser` hook should be used to ensure that the user is logged in be
 
 Replaceable (kind 10000-19999) and addressable (kind 30000-39999) events require a read-modify-write cycle: fetch the current event, modify its tags, then publish a new version. **Never read from TanStack Query cache before mutating** -- the cache can be stale from another device or a rapid prior operation, and republishing stale data silently drops the user's data.
 
-Use `fetchFreshEvent()` from `src/lib/fetchFreshEvent.ts` inside every mutation:
+Use `fetchFreshEvent()` from `src/lib/fetchFreshEvent.ts` inside every mutation, and **always pass the fetched event as `prev`** so `useNostrPublish` can preserve `published_at`:
 
 ```typescript
 import { fetchFreshEvent } from '@/lib/fetchFreshEvent';
 
 // Inside a mutation function:
-const freshEvent = await fetchFreshEvent(nostr, {
+const prev = await fetchFreshEvent(nostr, {
   kinds: [10003],
   authors: [user.pubkey],
 });
-const currentTags = freshEvent?.tags ?? [];
+const currentTags = prev?.tags ?? [];
 // ...modify tags...
-await publishEvent({ kind: 10003, content: freshEvent?.content ?? '', tags: newTags });
+await publishEvent({
+  kind: 10003,
+  content: prev?.content ?? '',
+  tags: newTags,
+  prev: prev ?? undefined,
+});
 ```
 
 This applies to all list-type hooks (bookmarks, pins, interests, follow sets, badges, etc.). See `useFollowActions` and `useMuteList` for complete examples.
 
+#### The `prev` Property on Event Templates
+
+`useNostrPublish` accepts an optional `prev` property on the event template. This is the **previous version** of the event being replaced. The hook uses it to automatically manage the `published_at` tag (NIP-24) for replaceable and addressable events:
+
+- **First publish (no `prev`)**: `published_at` is set equal to `created_at`
+- **Update (`prev` provided)**: `published_at` is preserved from the old event
+- **Old event lacks `published_at`**: nothing is fabricated
+- **Caller already set `published_at` in tags**: left alone
+
+**Convention**: Name the local variable `prev` at the call site (not `freshEvent` or `latestEvent`) so it reads naturally when passed to `publishEvent`:
+
+```typescript
+const prev = await fetchFreshEvent(nostr, { kinds: [3], authors: [user.pubkey] });
+// ...
+await publishEvent({ kind: 3, content: prev?.content ?? '', tags: newTags, prev: prev ?? undefined });
+```
+
+`prev` is stripped from the template before signing — it never appears in the published Nostr event.
+
 ### D-Tag Collision Prevention for Addressable Events
 
 Addressable events (kind 30000-39999) are identified by `pubkey + kind + d-tag`. Publishing an event with the same d-tag as an existing one **silently replaces** it. This is by design for intentional updates (edit flows), but dangerous when creating *new* content with user-derived d-tags (slugs from titles, user-entered identifiers, etc.).