feat: add 11 features and bug fixes across server, SDK, and client

Server fixes:
- Wire v2 moderation handlers to ModerationService (SQL persistence) —
  bans now survive restarts instead of living in-memory DashMap
- Add admin role enforcement via QPC_ADMIN_KEYS env var for ban/unban
- Fix audit.rs now_iso8601() to emit actual ISO-8601 timestamps
- Add group admin authorization — only creator can remove members or
  update metadata

Server features:
- Add DeleteBlob RPC (method 602) with filesystem cleanup
- Register delete_blob in v2 handler method registry

SDK features:
- Add ClientEvent::IdentityKeyChanged for safety number change alerts
- Add ClientEvent::ReadReceipt and DeliveryConfirmation variants
- Add peer_identity_keys table with store/get methods for key tracking
- Add search_messages() full-text search across all conversations
- Add delete_conversation() with cascading message/outbox cleanup

Client features:
- Wire v2 TUI message sending to SDK MLS encryption pipeline
- Add /search command to v2 REPL with cross-conversation results
- Add /delete-conversation command to v2 REPL
- Add unread count badges in v1 TUI sidebar (yellow+bold styling)

crates/quicprochat-sdk/src/conversation.rs

@@ -185,6 +185,13 @@ impl ConversationStore {
                 identity_key    BLOB PRIMARY KEY,
                 blocked_at_ms   INTEGER NOT NULL,
                 reason          TEXT NOT NULL DEFAULT ''
+            );
+
+            CREATE TABLE IF NOT EXISTS peer_identity_keys (
+                username        TEXT PRIMARY KEY,
+                identity_key    BLOB NOT NULL,
+                first_seen_ms   INTEGER NOT NULL,
+                last_seen_ms    INTEGER NOT NULL
             );",
         )
         .context("migrate conversation db")
@@ -524,6 +531,112 @@ impl ConversationStore {
         msgs.reverse();
         Ok(msgs)
     }
+
+    // ── Peer identity key tracking ──────────────────────────────────────────
+
+    /// Look up the stored identity key for a peer by username.
+    pub fn get_peer_identity_key(&self, username: &str) -> anyhow::Result<Option<Vec<u8>>> {
+        let key: Option<Vec<u8>> = self
+            .conn
+            .query_row(
+                "SELECT identity_key FROM peer_identity_keys WHERE username = ?1",
+                params![username],
+                |row| row.get(0),
+            )
+            .optional()?;
+        Ok(key)
+    }
+
+    /// Store (or update) a peer's identity key.  Returns the previous key if it changed.
+    pub fn store_peer_identity_key(
+        &self,
+        username: &str,
+        identity_key: &[u8],
+    ) -> anyhow::Result<Option<Vec<u8>>> {
+        let now_ms = std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_millis() as i64;
+
+        let old = self.get_peer_identity_key(username)?;
+
+        self.conn.execute(
+            "INSERT INTO peer_identity_keys (username, identity_key, first_seen_ms, last_seen_ms)
+             VALUES (?1, ?2, ?3, ?3)
+             ON CONFLICT(username) DO UPDATE SET identity_key = ?2, last_seen_ms = ?3",
+            params![username, identity_key, now_ms],
+        )?;
+
+        // Return the old key only if it's different from the new one.
+        match old {
+            Some(ref prev) if prev != identity_key => Ok(old),
+            _ => Ok(None),
+        }
+    }
+
+    // ── Full-text search ────────────────────────────────────────────────────
+
+    /// Search messages across all conversations by body text.
+    pub fn search_messages(
+        &self,
+        query: &str,
+        limit: usize,
+    ) -> anyhow::Result<Vec<SearchResult>> {
+        let pattern = format!("%{query}%");
+        let mut stmt = self.conn.prepare(
+            "SELECT m.conversation_id, c.display_name, m.sender_name, m.body,
+                    m.timestamp_ms, m.message_id
+             FROM messages m
+             JOIN conversations c ON c.id = m.conversation_id
+             WHERE m.body LIKE ?1
+             ORDER BY m.timestamp_ms DESC
+             LIMIT ?2",
+        )?;
+        let rows = stmt.query_map(
+            params![pattern, limit.min(u32::MAX as usize) as u32],
+            |row| {
+                let conv_id_raw: Vec<u8> = row.get(0)?;
+                let mut conv_id = [0u8; 16];
+                if conv_id_raw.len() == 16 {
+                    conv_id.copy_from_slice(&conv_id_raw);
+                }
+                Ok(SearchResult {
+                    conversation_id: ConversationId(conv_id),
+                    conversation_name: row.get(1)?,
+                    sender_name: row.get(2)?,
+                    body: row.get(3)?,
+                    timestamp_ms: row.get::<_, i64>(4)? as u64,
+                    message_id: row.get(5)?,
+                })
+            },
+        )?;
+        rows.collect::<Result<Vec<_>, _>>().map_err(Into::into)
+    }
+
+    // ── Conversation deletion ───────────────────────────────────────────────
+
+    /// Delete a conversation and all its messages.
+    pub fn delete_conversation(&self, id: &ConversationId) -> anyhow::Result<bool> {
+        self.conn
+            .execute("DELETE FROM messages WHERE conversation_id = ?1", params![id.0.as_slice()])?;
+        self.conn
+            .execute("DELETE FROM outbox WHERE conversation_id = ?1", params![id.0.as_slice()])?;
+        let rows = self
+            .conn
+            .execute("DELETE FROM conversations WHERE id = ?1", params![id.0.as_slice()])?;
+        Ok(rows > 0)
+    }
+}
+
+/// A search result across conversations.
+#[derive(Clone, Debug)]
+pub struct SearchResult {
+    pub conversation_id: ConversationId,
+    pub conversation_name: String,
+    pub sender_name: Option<String>,
+    pub body: String,
+    pub timestamp_ms: u64,
+    pub message_id: Option<Vec<u8>>,
 }
 
 // ── Helpers ──────────────────────────────────────────────────────────────────