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.

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -2227,7 +2227,7 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'SubprocessHandle',
-    declaration: 'export interface SubprocessHandle {\n    readonly pid: number;\n    readonly stdin: Writable | undefined;\n    readonly stdout: Readable | undefined;\n    readonly stderr: Readable | undefined;\n    readonly collected: SubprocessCollectedOutputs;\n    readonly done: Promise<SubprocessOutcome>;\n    kill(signal?: NodeJS.Signals): void;\n    terminate(): void;\n    waitForExit(signal?: AbortSignal): Promise<boolean>;\n    dispose(graces: SubprocessDisposeGraces): Promise<void>;\n}',
+    declaration: 'export interface SubprocessHandle {\n    readonly pid: number;\n    readonly stdin: Writable | undefined;\n    readonly stdout: Readable | undefined;\n    readonly stderr: Readable | undefined;\n    readonly collected: SubprocessCollectedOutputs;\n    readonly done: Promise<SubprocessOutcome>;\n    terminate(): void;\n    waitForExit(signal?: AbortSignal): Promise<boolean>;\n    dispose(graces: SubprocessDisposeGraces): Promise<void>;\n}',
   },
   {
     name: 'SubprocessOutcome',