fix(web): review round 1 — loud opt-out, headless drain, scaffold isolation, docs

- resolveTelemetryPatch: extracted pure switch resolution (unit-tested);
  fails loud when DSH_TELEMETRY_DISABLED is set but the row is absent, and
  documents that ANY non-empty value (including '0'/'false') disables.
- runHeadless: SIGINT/SIGTERM now dispose the tree before exit so the
  telemetry tail and shutdown marker drain (Node's default signal exit
  skips disposal).
- web.cordis.yml: explicit maxQueueSize beside maxExportBatchSize (the
  single-batch drain invariant no longer leans on an SDK default), comment
  covers exportTimeoutMillis's role and links the Agent Note.
- apps/web scaffold: disable telemetry-otel — fixture sessions must never
  leave the process.
- apps/cli README (en/zh + pairing): document the default endpoint, both
  env seams, and the no-redaction disclosure.

apps/cli/tests/telemetry-switch.spec.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest'
+import { resolveTelemetryPatch } from '../src/app-cli-entry.ts'
+
+describe('resolveTelemetryPatch', () => {
+  it('keeps telemetry enabled when the switch is unset or empty', () => {
+    expect(resolveTelemetryPatch(undefined, true)).toBeUndefined()
+    expect(resolveTelemetryPatch('', true)).toBeUndefined()
+  })
+
+  it('disables on ANY non-empty value, including falsy-looking ones', () => {
+    for (const value of ['1', '0', 'false', 'no']) {
+      expect(resolveTelemetryPatch(value, true)).toEqual({ id: 'telemetry-otel', disabled: true })
+    }
+  })
+
+  it('fails loud when the switch is set but the row is absent', () => {
+    expect(() => resolveTelemetryPatch('1', false)).toThrow('DSH_TELEMETRY_DISABLED is set but row "telemetry-otel" is not in this composition')
+  })
+
+  it('ignores a missing row while the switch is unset', () => {
+    expect(resolveTelemetryPatch(undefined, false)).toBeUndefined()
+  })
+})