Adds every remaining wire variant and RPC needed to finish the Telegram-quality
mesh plan in a single pass:
* Variants 15 ReadReceipt, 16 Forward, 17 Edit, 18 Delete, 20 Presence,
21 ChannelInvite; plus MeshMessageType::ContactCard(22) cleanup (was
enum-only, now wired through from_u8/label/from_label).
* MessageType::from_label() as the inverse of label() — used by the Forward
path to re-encode a stored typed body back through its original variant.
* RPCs: mesh.send-psbt (variant 3 was previously enum-only),
mesh.send-read-receipt, mesh.forward-message, mesh.edit-message,
mesh.delete-message, mesh.broadcast-presence, mesh.presence-list,
mesh.contacts-list, mesh.contacts-save, mesh.contacts-block,
mesh.send-channel-invite, conversations.list, conversations.messages.
* MeshState gains presence (pubkey → status+timestamps) and contacts
(pubkey → ContactEntry{alias,notes,pinned,blocked}) in-memory stores.
* MeshService gains find_message_by_id (Forward lookup), apply_local_edit /
apply_local_delete (optimistic local echo), and send_chunked_payload — an
MC-framed base64 splitter that fires as a fallback inside send_typed_wire
when wire > MAX_MESSAGE_LEN and no federation path is known. Reuses the
existing receive-side reassembly in listener/decode.rs.
* Receive dispatch arms for PsbtHash, Presence, ChannelInvite, ReadReceipt
(rolls forward `delivered` flag on own-Sent ≤ seq for that peer), Forward,
Edit, Delete. Edit/Delete guard against cross-peer tampering by matching
the target MessageKey pubkey against the sender's advertised pubkey_hex.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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