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/data/address_book.h

@@ -4,6 +4,7 @@
 
 #pragma once
 
+#include <cstdint>
 #include <string>
 #include <vector>
 
@@ -121,11 +122,18 @@ public:
      */
     size_t size() const { return entries_.size(); }
 
+    /**
+     * @brief Monotonic counter bumped on every content change (add/update/remove/load/sweep). Consumers
+     * (e.g. the chat conversation-list memo) key their caches off this so an IN-PLACE edit — a rename or
+     * address change that keeps size() constant — still invalidates them.
+     */
+    std::uint64_t revision() const { return revision_; }
+
     /**
      * @brief UI-sweep ONLY: replace the in-memory entries WITHOUT persisting to disk, so the sweep can
      * seed demo contacts and restore the real book without a disk write. Do not use outside the sweep.
      */
-    void sweepSetEntries(std::vector<AddressBookEntry> e) { entries_ = std::move(e); }
+    void sweepSetEntries(std::vector<AddressBookEntry> e) { entries_ = std::move(e); ++revision_; }
 
     /**
      * @brief Check if empty
@@ -134,6 +142,7 @@ public:
 
 private:
     std::vector<AddressBookEntry> entries_;
+    std::uint64_t revision_ = 0;
     std::string file_path_;
 };