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/web/tests/scaffold.ts

@@ -221,6 +221,10 @@ export async function launchWebScaffold(options: LaunchOptions = {}): Promise<We
     // workspace, keeping the composition untouched.
     { id: 'workspace-context', disabled: true },
     { id: 'session-title-llm', disabled: true },
+    // Fixture sessions must never leave the process: the shipped row defaults
+    // to the production OTLP endpoint (or whatever DSH_TELEMETRY_OTLP_URL
+    // names in the ambient environment).
+    { id: 'telemetry-otel', disabled: true },
     { id: 'webserver', config: { host: '127.0.0.1', port: 0, distIndex: DIST_INDEX } },
     { id: 'settings', config: { dshHome: harnessHome } },
     { id: 'credentials', config: { dshHome: harnessHome } },