refactor(pty): rename model-facing tools to terminal_* and harden teardown

Rename the six model-facing tools pty_* -> terminal_* and align every
description, guidance section, ACP card title, and rendered result to
terminal terminology. Package and service internals keep their technical
PTY names (PtyService, "unknown PTY session", node-pty).

Harden the local backend teardown:
- a failed close is retryable: drop the memoized rejection so a later
  terminal_close re-runs against the live process table
- service disposal clears the backend, reservation, and owner-cleanup
  registries even when a close fails
- stop readiness polling before teardown so an in-flight send settles as
  session_exit instead of a mis-inferred wait reason
- bound the sanitizer's pending buffer against unterminated escape runs

Update the tool catalog, package READMEs, the bilingual Agent Note, and the
acp/headless pty-tools snapshots to match.

docs/core-data-structures/pty.md

@@ -37,7 +37,7 @@ interface PtyBackend {
 ```ts type-equiv
 /** Backend-owned live session retained by {@link PtyService}. */
 interface PtyBackendSession {
-  /** Initial bounded terminal output returned from `pty_spawn`. */
+  /** Initial bounded terminal output returned from `terminal_open`. */
   readonly motd: string
   /** Top-level process id when one exists. */
   readonly pid?: number