refactor(subprocess): keep terminate() as the seam's only termination verb

Delete kill(signal?) from SubprocessHandle: consumers stop a process only
through terminate()'s tree-scoped SIGTERM→graceMs→SIGKILL escalation
(idempotent, also driven by the spec's abort signal, a no-op once the tree
is gone). The single-signal verb had exactly one consumer family —
lsp-local — and what it bought there was a private re-implementation of
the same escalation. The internal kill closure stays in spawn.ts as the
dispose ladder's tier primitive; terminate() now routes through it too.

lsp-local collapses onto the seam's escalation:
- LspConnection replaces its terminate()/kill() pair with one terminate()
  that delegates to handle.terminate(). Behavior change: the
  framing-failure path terminates instead of instant SIGKILL, so a
  misbehaving server now gets SIGTERM plus the killGraceMs window to
  flush before SIGKILL.
- ConnectionSpec.pipeDrainGraceMs becomes killGraceMs: one grace, the
  spawn spec's graceMs, drives both the escalation window and post-exit
  pipe draining (the provider already passed killGraceMs for it).
- LspInstance.forceTerminate() drops its hand-rolled bounded first wait
  (LSP_KILL_GRACE) and escalateProcessTree (deleted with its export and
  unit test): the seam's escalation already commits to SIGKILL after
  killGraceMs, so only the unbounded quiescence awaits stay load-bearing.

Tests: kill()-shaped spawn specs become terminate()-shaped or fold into
the terminate() suites (group-wide delivery; the settled no-op case was
already pinned by 'terminate() after the tree died'); tree-survivor
coverage is intact. A stderr-'inherit' disposition test completes the
stdout/stderr symmetry so the scoped subprocess+lsp coverage gate stands
alone instead of leaning on subagent-acp's cross-package runs.

Docs: SubprocessHandle type-equiv block, seam/impl/group READMEs, and the
consumer-migration Agent Note lose the kill(signal?) vocabulary (zh pairs
re-recorded); cordis api/services catalogs regenerated.

docs/core-data-structures/subprocess.md

@@ -132,7 +132,7 @@ interface SubprocessSpawnSpec {
 
 ## Handles: streams, readers, and tree-scoped termination
 
-A spawn returns a live handle immediately. Collect-mode readers take whole-stream byte offsets and never consume, so independent readers cannot steal one another's deltas; piped streams belong to the caller. Termination is tree-scoped on every platform: `kill(signal)` sends one signal Node-style, `terminate()` escalates SIGTERM→grace→SIGKILL, `waitForExit()` observes the whole tree, and `dispose(graces)` runs the cooperative stdin-EOF→SIGTERM→SIGKILL ladder out-of-process children need.
+A spawn returns a live handle immediately. Collect-mode readers take whole-stream byte offsets and never consume, so independent readers cannot steal one another's deltas; piped streams belong to the caller. Termination is tree-scoped on every platform: `terminate()` — the only termination verb — escalates SIGTERM→grace→SIGKILL, `waitForExit()` observes the whole tree, and `dispose(graces)` runs the cooperative stdin-EOF→SIGTERM→SIGKILL ladder out-of-process children need.
 
 ```ts type-equiv
 /**
@@ -157,17 +157,11 @@ interface SubprocessHandle {
   readonly collected: SubprocessCollectedOutputs
   /** Resolves at process close with exit facts; rejects only for spawn-level failures. */
   readonly done: Promise<SubprocessOutcome>
-  /**
-   * Send one signal to the process tree, Node-style — no escalation, no
-   * timers. A no-op after the outcome has settled (the pid may be reused).
-   * @param signal - the signal to deliver (default `SIGTERM`; Windows
-   *   force-terminates the tree for any value).
-   */
-  kill(signal?: NodeJS.Signals): void
   /**
    * Begin the SIGTERM → `graceMs` → SIGKILL escalation on the process tree
-   * (Windows force-terminates immediately). Idempotent; also triggered by the
-   * spec's abort signal.
+   * (Windows force-terminates immediately) — the seam's only termination
+   * verb. Idempotent, a no-op once the tree is gone (the pid may be reused),
+   * and also triggered by the spec's abort signal.
    */
   terminate(): void
   /**