feat(sync): :gl pull — fetch + fast-forward only on the git thread

The git channel now carries GitRequest::{Publish,Pull} with a shared
ensure_online preamble (Wi-Fi/clock/TLS once per session). pull_once
fetches origin — refreshing the tracking ref so the radio-free
up-to-date check stays honest — and maps four shapes: up to date,
LocalAhead (stranded commit, :sync's job), clean fast-forward,
Diverged (refused; no merge on the device). The fast-forward is a SAFE
checkout then ref move: it refuses to overwrite content that differs
from HEAD, the belt under the UI gate that refuses :gl while the dirty
journal is non-empty. A RAM-dirty buffer doesn't gate — its edits win
(last-writer-wins, like the reconcile).

After a pull the UI drops clean parked buffers, re-reads the clean
active buffer in place (Editor::refresh_active), and re-walks the
palette list. Firmware 0.6.0 -> 0.7.0. On-device verification pending.

firmware/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "firmware"
-version = "0.6.0"
+version = "0.7.0"
 authors = ["Julien Calixte <juliencalixte@gmail.com>"]
 edition = "2024"
 resolver = "2"