feat(chat): per-conversation delete (revive + block); memoize chat/badge render

Adds a per-conversation "delete" with two modes, and removes the per-frame
rescans of the chat history that shared these files.

Delete conversation (header trash icon → confirm dialog):
- Delete (revive-on-new-message): clears local history and tombstones the
  messages (new chat_deleted table, keyed dedup hashes) so the every-few-
  seconds memo re-scan can't re-import them; a genuinely NEW message (new
  txid) revives the thread.
- Delete & block: removes history WITHOUT a tombstone and records the cid as
  blocked (settings); ChatService::ingest drops that conversation's messages
  — old and future — until unblocked from the "Blocked" manager, which then
  re-imports the conversation from chain.
- Local-only (messages remain on-chain; the peer keeps their copy).
  deleteConversation() deletes the DB rows FIRST and only then mutates the
  store, so a failed write can't leave the two diverged.
Unit-tested (revive / tombstone-survives-reload / block / unblock) and
adversarially reviewed (store/DB divergence, half-open DB, revive-unread).

Performance (chat + badge hot paths, from the perf audit):
- ChatStore gains revision(); the Chat unread badge is now a single O(N)
  no-alloc pass cached on it (was O(conversations x messages) copy+sort every
  frame). The conversation list and open thread are memoized on revision()
  (+ show-hidden and AddressBook::revision() for peer-name resolution).
- AddressBook gains revision() so an in-place contact rename invalidates the
  chat memo (an edit keeps entries().size() constant).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -760,6 +760,22 @@ private:
     // wallets. In-memory only (resets on app restart).
     std::map<std::string, std::int64_t> chat_seen_watermark_;
 
+    // ── Per-frame render caches (avoid O(N) recompute every frame; see the respective call sites) ──
+    // Chat nav-badge unread count — recomputed only when the store revision changes or after a short
+    // interval (mute/hide/seen changes don't bump the store). See App::chatUnreadCount().
+    mutable std::uint64_t chat_unread_rev_ = ~0ull;   // ~0 forces the first compute
+    mutable int    chat_unread_cached_ = 0;
+    mutable double chat_unread_computed_at_ = 0.0;
+    // Sidebar unconfirmed-tx badge — recomputed only when the tx list changes (keyed on last_tx_update +
+    // size), not every frame. See App::render().
+    std::int64_t sb_unconf_key_ts_ = -1;
+    std::size_t  sb_unconf_key_n_  = 0;
+    int          sb_unconf_count_  = 0;
+    // Daemon-memory probe is expensive (/proc scan on Linux, popen on macOS); throttle it to ~1.5s so the
+    // Mining tab's per-frame read doesn't hammer the OS. See App::getDaemonMemoryUsageMB().
+    mutable double daemon_mem_cached_mb_ = 0.0;
+    mutable double daemon_mem_probe_at_  = 0.0;
+
     // ── Chat note buffer (BOTH variants) ────────────────────────────────────────────────────────
     // Each chat message is a shielded tx that spends a note; its change needs a few confirmations before
     // it's spendable again (lite: backend ANCHOR_OFFSET+1 = 5; full node: z_sendmany minconf = 1), so
@@ -835,6 +851,9 @@ public:
     int chatUnreadCount() const;
     // Mark a conversation read up to latestTs (called by the Chat tab while a thread is displayed).
     void markChatConversationSeen(const std::string& cid, std::int64_t latestTs);
+    // Drop the seen-watermark for a conversation (used on revive-delete so a re-imported message — even one
+    // whose stamped time predates the deleted thread's last message — still badges as unread).
+    void forgetChatConversationSeen(const std::string& cid);
 private:
     // Provision the chat identity once the wallet seed is reachable+unlocked (per-tick, both
     // variants); derives via deriveChatIdentityFromSecret and wipes the secret. No-op when the