fix(cursor): use Agent CLI build id for x-cursor-client-version

[andrewmunsell]

AgentService/Run impersonation was sending cli-${getCursorVersion()}, which reads the Cursor IDE state.vscdb (or FALLBACK_VERSION "3.9"). That produces wire values like cli-3.9 / cli-3.10.20.

History: pre-v3.8.0 the executor impersonated the IDE (x-cursor-client-type: ide, bare 3.x version, Cursor/UA + checksum). The v3.8.0 Agent Run migration switched to CLI-shaped headers (connect-es, client-type: cli) but reused the IDE detector and only prefixed cli-. Real cursor-agent embeds a dated build id (e.g. cli-2026.07.08-0c04a8a). Later UA refreshes (#5237) kept bumping the IDE pin, so the mismatch persisted.

Add getCursorAgentCliVersion(): CURSOR_AGENT_CLI_VERSION env, then local install detect (~/.local/bin shim realpath or versions dir / CURSOR_DATA_DIR), else pin 2026.07.08-0c04a8a. Keep IDE getCursorVersion() for checksum/registry paths. Align cursor-tap and document the new env var.

Validation

• npm run lint
• npm run test:unit
• npm run test:coverage
• Manually validated headers were updated with the Cursor CLI version string