Re-verify the wire contract at Grappa v1.5.12 and refresh the baseline

[Sythos]

Closes #239

Branch: docs-issue-239

Re-read the wire contract at Grappa v1.5.12 (commit c26c77bc, the first release speaking protocol 37) and refreshed the baseline in the docs.

What I checked at the tag

• @protocol_version 37, @min_protocol_version 1 in lib/grappa/protocol.ex.
• Scrollback row: dm_with optional, no dm_conversation_id. query_windows_list entry: network_id, target_nick, opened_at. mentions_bundle rows: id and dm_with optional.
• The docs/CLIENT_PROTOCOL.md diff since 189aaf2c: everything that touches Cordiale (v31 ignore pairs, v32 away nick suffix, v33 network delete + message_count, v34-v37 DM changes) is already in the code.
• GET /api/config on the author's server answers version 1.5.12, protocol 37.

What changed

• docs/protocol-notes.md, docs/feature-matrix.md: new baseline (v1.5.12), the "not verified against a real v35/v36/v37 server" notes now say what was checked at the source and what is still untested in a live session.
• crates/cordiale-core/src/protocol.rs: comment only.

Decisions on the leftovers (no code change)

• Own-nick window counts after our own nick change: Cicchetto keys the count on (network, current own nick) and ignores the payload's channel; the server sets channel to the topic segment. Cordiale rejoins the own-nick listener with the new nick on own_nick_changed, so the comparison holds. Only a push on the old topic before the rejoin is dropped (Cicchetto would route it to the new nick), which is transient and harmless. The count doesn't classify rows, so dm_with isn't needed.
• Self-KICK rejoin (upstream #2321): server-side only. Cordiale already keeps kicked/joined/join_failed as window states with a faded sidebar row, including from a reconnect snapshot.
• Wide rows (upstream #2310): rows are wrapping StyledText in a ListView with no explicit clip. No local build here, so a long line without spaces still needs an eyeball check on desktop; noted in the feature matrix.

Live flows (DM routing after a rename, mentions bundle, admin network delete with message_count) stay for a hand test against a real v1.5.12 session.