feat(mesh): native-unicast DMs, contact import/remove, reachability, contact search

- DMs now use native meshcore unicast (CMD_SEND_TXT_MSG) instead of @DM2 channel
  broadcasts: private (E2E-encrypted to the recipient pubkey by firmware), off the
  public channel, and decodable by stock clients. Plain text (split, not MC-chunked)
  to non-archipelago contacts; typed envelopes to archy peers.
- !ai replies now DM the asker privately (RadioDm) instead of broadcasting on ch0.
- Auto contact-import: a heard advert (PUSH_CONTACT_ADVERT/0x80, 32-byte pubkey) is
  added via CMD_ADD_UPDATE_CONTACT (0x09) so contacts appear without a flood advert.
- clear-all now DELETES firmware contacts via CMD_REMOVE_CONTACT (0x0F) instead of
  blocklisting; blocking filter removed entirely. Wiped contacts return when reachable.
- Contact reachability: MeshPeer carries last_advert + reachable (path-based); UI shows
  a reachability dot.
- Peers list: contact search box (filter by name/DID/npub/pubkey) with a clear button.
- send_message routes stock contacts as plain native text (fixes garbled envelopes).

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

core/archipelago/src/mesh/protocol.rs

@@ -30,6 +30,13 @@ pub const CMD_SYNC_NEXT_MESSAGE: u8 = 0x0A;
 /// known" — without this, the firmware silently drops outbound TXT_MSG
 /// frames to such contacts.
 pub const CMD_RESET_PATH: u8 = 0x0D;
+/// CMD_ADD_UPDATE_CONTACT (0x09): add or update a contact in the firmware
+/// table. 144-byte frame (see `build_add_contact`).
+pub const CMD_ADD_UPDATE_CONTACT: u8 = 0x09;
+/// CMD_REMOVE_CONTACT (0x0F): `[0x0F][pub_key:32]` — delete a contact from the
+/// firmware's persistent table (used by clear-all so wiped contacts actually
+/// go away and only return when they re-advertise).
+pub const CMD_REMOVE_CONTACT: u8 = 0x0F;
 pub const CMD_SET_RADIO_PARAMS: u8 = 0x0B;
 pub const CMD_SET_RADIO_TX_POWER: u8 = 0x0C;
 pub const CMD_SET_TUNING_PARAMS: u8 = 0x15;
@@ -258,6 +265,45 @@ pub fn build_reset_path(pubkey: &[u8; 32]) -> Vec<u8> {
     encode_frame(&data)
 }
 
+/// CMD_REMOVE_CONTACT (0x0F): `[0x0F][pub_key:32]`. Removes the contact from
+/// the firmware's persistent contact table.
+pub fn build_remove_contact(pubkey: &[u8; 32]) -> Vec<u8> {
+    let mut data = vec![CMD_REMOVE_CONTACT];
+    data.extend_from_slice(pubkey);
+    encode_frame(&data)
+}
+
+/// CMD_ADD_UPDATE_CONTACT (0x09): add/update a contact. 144-byte body:
+/// `[0x09][pub_key:32][type:1][flags:1][out_path_len:1][out_path:64][name:32]
+///  [last_advert:4 LE][adv_lat:4 LE][adv_lon:4 LE]`.
+/// `name` is zero-padded to 32 bytes (the firmware fills it from the heard
+/// advert on its side too, so an empty name still resolves on get-contacts).
+pub fn build_add_contact(
+    pubkey: &[u8; 32],
+    contact_type: u8,
+    flags: u8,
+    out_path_len: u8,
+    name: &str,
+    last_advert: u32,
+) -> Vec<u8> {
+    let mut data = Vec::with_capacity(144);
+    data.push(CMD_ADD_UPDATE_CONTACT);
+    data.extend_from_slice(pubkey); // 32
+    data.push(contact_type); // 1
+    data.push(flags); // 1
+    data.push(out_path_len); // 1
+    data.extend_from_slice(&[0u8; 64]); // out_path (64)
+    let mut name_buf = [0u8; 32];
+    let nb = name.as_bytes();
+    let n = nb.len().min(32);
+    name_buf[..n].copy_from_slice(&nb[..n]);
+    data.extend_from_slice(&name_buf); // name (32)
+    data.extend_from_slice(&last_advert.to_le_bytes()); // last_advert (4)
+    data.extend_from_slice(&0i32.to_le_bytes()); // adv_lat (4)
+    data.extend_from_slice(&0i32.to_le_bytes()); // adv_lon (4)
+    encode_frame(&data)
+}
+
 /// CMD_SYNC_NEXT_MESSAGE (0x0A): Retrieve the next queued message.
 pub fn build_sync_next_message() -> Vec<u8> {
     encode_frame(&[CMD_SYNC_NEXT_MESSAGE])