feat(telemetry): anonymous usage telemetry — documented schema, opt-out, public ingest worker (#834)

Adds anonymous usage statistics (commands/tools used, languages indexed,
connecting agents) with a strict, auditable allowlist. Never code, paths,
file/symbol names, queries, or IPs.

- src/telemetry/: zero-dep client — consent resolution (DO_NOT_TRACK >
  CODEGRAPH_TELEMETRY > stored choice > default-on), random machine UUID,
  in-memory counters → capped JSONL buffer → completed-day rollups; sync
  exit-append (survives process.exit) + opportunistic bounded sends; the
  first-run notice gates the first SEND, never local buffering, so the
  installer's consent toggle always precedes it. Off is off: no recording,
  no socket, buffered data deleted.
- codegraph telemetry status|on|off; per-command counting via preAction hook.
- MCP: tool counting after the reply is on the wire (session + proxy
  in-process fallback), agent attribution from initialize clientInfo,
  unref'd daemon flush interval. Zero hot-path cost, zero stdout.
- Installer: visible default-on consent toggle (asked once, never re-asked),
  install/index/uninstall lifecycle events.
- telemetry-worker/: public Cloudflare Worker behind telemetry.getcodegraph.com
  — allowlist validation, IP stripping, per-machine rate limit, forwards to
  PostHog as anonymous events. Ships nowhere with the npm package.
- TELEMETRY.md (field-by-field contract) + README section + design doc.
- 20 unit tests; suite-wide CODEGRAPH_TELEMETRY=0 guard so tests never
  pollute real telemetry. Full suite: 1448 passing.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -589,6 +589,23 @@ add a negation — `!vendor/`. The defaults apply uniformly, so committing a
 dependency or build directory doesn't force it into the graph; the `.gitignore`
 negation is the explicit opt-in.
 
+## Telemetry
+
+CodeGraph collects **anonymous usage statistics** — which tools and commands get
+used, which languages get indexed — to guide where language and agent support
+work goes. **Never** any code, paths, file or symbol names, queries, or IP
+addresses; usage is aggregated locally into daily totals before anything is
+sent, and the ingest endpoint is [public code in this repo](telemetry-worker/)
+that enforces the documented field list. The installer asks up front; turn it
+off any time:
+
+```bash
+codegraph telemetry off    # or: CODEGRAPH_TELEMETRY=0, or DO_NOT_TRACK=1
+```
+
+[`TELEMETRY.md`](TELEMETRY.md) lists every field, with the off-switches and the
+full data-handling story.
+
 ## Supported Platforms
 
 Every release ships a self-contained build (bundled Node runtime — nothing to