fix(pty): keep the controlled prompt so persistent bash settles fast

tool-bash-persistent overwrote the backend's PS1, so terminal-bash prompt
readiness never matched and every send degraded to the 3.5s silence tier
(idleSilenceMs + handoffGraceMs) under production defaults.

The controlled PROMPT_COMMAND now re-asserts PS1 before every prompt, so an
in-shell override never survives to the next prompt. The tool initializes
with stty -echo alone and detects the no-end-marker fallback through the
seam's stdin_read wait reason instead of matching its own prompt text.

Tool calls drop from 7180/3560/3566 ms to 355/88/91 ms (spawn+init+echo,
echo, pwd; darwin, production defaults). The loader composition suite now
pins the fast path by pushing idleSilenceMs beyond the send bound, and a
real-PTY case proves PS1 self-healing.

Fixes #2585

docs/config-catalog.md

@@ -2370,7 +2370,7 @@ export interface Config {
 }
 ```
 
-Source: [`packages/shell/tool-bash-persistent/src/index.ts:405`](../packages/shell/tool-bash-persistent/src/index.ts)
+Source: [`packages/shell/tool-bash-persistent/src/index.ts:400`](../packages/shell/tool-bash-persistent/src/index.ts)
 
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