fix(pi): read pi's composer rule so a pi turn can end

A pi session stayed "working" for good once a turn started. pi's braille
spinner trips the SPINNER_PATTERN fast path, which marks the pane working,
but only a composer glyph arms the idle confirmation and pi declared none,
so it fell back to Claude's `❯`, which pi never draws. Measured on beta136:
an errored turn stayed busy/isWorking for 3+ minutes after pi was back at
rest.

pi has no composer glyph. Measured on a live pi 1.1.0 pane (capture-pane
every 250 ms through a turn): its composer sits between two `─` rules, and
while a turn runs it rewrites the top rule as `── ⠏ Working ───` on every
frame. The registry entry now names the rule as the glyph that arms the
check and a spinner frame inside it as the working line.

The same glyph settles a reattached pi pane (a restored pane gets no launch
timer): tmux's reattach repaint carries `─`, which arms the confirmation.
The submit verifier reads the last rule, finds no prompt text and stands
down, so it can never press Enter on a pi pane.

Verified on an isolated instance from this branch: a real pi turn emitted
session:working then session:idle, and after a server restart the restored
pi pane went busy -> idle in about 3 s.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/pi-integration.md

@@ -223,9 +223,13 @@ command override instead.
 ## Known gaps
 
 - **No idle/completion hook.** Pi has no hook system Codeman can install into, so
-  idle detection falls back to output-stabilization like the other external CLIs.
-  Pi 0.84.0 shipped an `agent_settled` extension event that is a genuine idle
-  signal; a Codeman pi extension using it is the highest-value follow-up.
+  idle detection reads the screen: the registry entry's `workDetect` names pi's
+  composer rule (`─`) as the glyph that arms the idle check and the spinner pi embeds
+  in that rule while a turn runs (`── ⠏ Working ───`) as the working line, measured
+  on pi 1.1.0. Without it a pi session that had started a turn never left `busy`,
+  since pi never draws Claude's `❯`. Pi 0.84.0 shipped an `agent_settled` extension
+  event that is a genuine idle signal; a Codeman pi extension using it is still the
+  highest-value follow-up.
 - **No response viewer.** Pi writes JSONL v3 session files under
   `~/.pi/agent/sessions/`; nothing reads them yet.
 - **Cron jobs mis-detect readiness.** The cron readiness poll looks for `❯` or a