feat: add PostHog telemetry for CLI errors and warnings (#3242)

Sends CLI errors, warnings, and crashes to PostHog for observability.
Strictly error/warning events — no command tracking or session events.

All messages are scrubbed before sending:
- API keys (sk-or-v1-*, sk-ant-*, key-*)
- GitHub tokens (ghp_*, github_pat_*)
- Bearer tokens
- Email addresses
- IP addresses
- Long tokens (60+ char alphanumeric)
- Base64 blobs (40+ chars)
- Home directory paths (/Users/name → ~/[USER])

Default on. Disable with SPAWN_TELEMETRY=0.
Fire-and-forget with 5s timeout — never blocks the CLI.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@openrouter/spawn",
-  "version": "0.31.5",
+  "version": "0.32.0",
   "type": "module",
   "bin": {
     "spawn": "cli.js"