docs: source badge name only, no signals lock, the Add-a-signal page

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/invariants-session-and-export.md

@@ -13,9 +13,9 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   (`rebuild_trigger_signals()` picks up `App::pending_trigger_channel`, or `apply_trigger_layout()`
   resolves it itself when they are already there) — a name that resolved to nothing would silently move
   the trigger to channel 0.
-- **A session that loaded is what locks the two panes.** Locked is the returning user's mode: the
-  trigger pane shows one compact line, the signal list only the signals that are on, and neither offers
-  a control that changes the configuration. A *first run* — no session file for that source — never
+- **A session that loaded is what locks the trigger pane.** Locked is the returning user's mode: the
+  trigger pane shows one compact line and offers no control that changes the configuration (the signals
+  have no lock). A *first run* — no session file for that source — never
   reaches `apply_layout()` and stays in configuration mode, which is what a first run is for. The mode
   is a mode and not a setting: it is deliberately not persisted, so a scope reopened tomorrow starts
   where a returning user expects to start. **Dragging a signal onto a plot is not configuration and survives