channels: improve tmux state tracking and config persistence

tmux channel:
- Track connected state per-pane (shows true channel availability)
- Persist pane config on add/remove (survives restarts)
- Remove cleanup_pipes on exit (unnecessary with persisted config)
- Reorder PaneConfig fields for consistency

telegram channel:
- Use json5 crate for config parsing (matches tmux)

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

channels/telegram/Cargo.toml

@@ -8,6 +8,7 @@ capnp = "0.25"
 capnp-rpc = "0.25"
 dirs = "6"
 futures = "0.3"
+json5 = "1.3"
 consciousness = { path = "../.." }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"