fix: remove deleted rooms from space navigation after refresh

## Summary

This PR fixes a bug where deleting a room succeeded on the relay, but the room could still appear in space navigation (including after refresh).

Fixes #194.

## Root Cause

Room list derivation did not consistently treat delete events as authoritative in edge cases:
- Delete timestamp aggregation could involve an undefined prior value.
- Room meta events with the same second-level timestamp as a delete event were still considered active.

## Changes

- Updated room delete timestamp aggregation logic to handle first delete event safely.
- Updated room filtering condition so a room is excluded when its meta timestamp is less than or equal to the delete timestamp.
- This ensures deleted rooms are not shown in navigation immediately or after reload.

## Validation

- `pnpm run check` passed.
- `pnpm run lint` passed.

## Testing

- [x] In a NIP-29 space, create a temporary room.
- [x] Delete the room from room details.
- [x] Confirm it disappears from navigation immediately.
- [x] Hard refresh and confirm it does not reappear.
- [x] Reopen app/session and confirm it remains absent.
- [x] Repeat by creating/deleting another room quickly (same-minute timestamp edge case).

src/app/core/state.ts

@@ -615,7 +615,12 @@ export const roomsByUrl = derived(roomMetaEventsByIdByUrl, roomMetaEventsByIdByU
 
     for (const event of deleteEvents) {
       for (const h of getTagValues("h", event.tags)) {
-        deletedByH.set(h, max([deletedByH.get(h), event.created_at]))
+        const deletedAt = deletedByH.get(h)
+
+        deletedByH.set(
+          h,
+          deletedAt === undefined ? event.created_at : max([deletedAt, event.created_at]),
+        )
       }
     }
 
@@ -623,8 +628,9 @@ export const roomsByUrl = derived(roomMetaEventsByIdByUrl, roomMetaEventsByIdByU
 
     for (const event of metaEvents) {
       const meta = tryCatch(() => readRoomMeta(event))
+      const deletedAt = meta ? deletedByH.get(meta.h) : undefined
 
-      if (!meta || gt(deletedByH.get(meta.h), meta.event.created_at)) {
+      if (!meta || (deletedAt !== undefined && !gt(meta.event.created_at, deletedAt))) {
         continue
       }