fix(skill): align telemetry dispatch and field name with server

[lxcong]

Summary

PR #31 wired skill-side telemetry through two paths that don't actually
connect, so zero usable events reach PostHog from a real LLM session.

• Bug 1 (dispatch path): SKILL.md told the LLM
  execute_tool(name="agentkey_internal", params={...}), but
  agentkey_internal is registered as a separate top-level MCP tool in
  @agentkey/mcp ≥0.3.10. execute_tool's router only knows
  agentkey_search / scrape / social / crypto, so the call returned
  tool not found and SKILL.md's silent-fallback swallowed the error.

• Bug 2 (field name): Body wrapped properties under props: {...}
  but internal/handler/telemetry_handler.go decodes
  Properties map[string]interface{} json:"properties". Mismatched tag
  → nil map → server substituted empty map → every business field
  stripped before reaching PostHog. Only posthog-go's auto-injected
  $lib / $os / $ip plus agent: "unknown" (from
  NormalizeAgent("")) survived.

Evidence

Direct call vs SKILL.md-shaped call, same distinct_id, minutes apart in
PostHog (project agentkey):

body field name	PostHog record for upgrade_decision
properties: {...} ✅	from_version=1.5.0, to_version=1.6.0, choice=accept_once, agent=claude-code — all fields
props: {...} ❌	All None

Sink / auth / posthog-go batching / 24h dedupe all confirmed fine. Bug
surface is exactly the two items above.

Changes

SKILL.md only:

• 6 dispatch sites: execute_tool(name="agentkey_internal", params={...})
  → agentkey_internal({...})
• Body field: props → properties

No change to check-update.sh, MCP forwarder, or server. Skill-only is
the cheaper side to align: 1.6.0 just shipped and has no install base.

Agent attribution (server falling back to agent: "unknown") is left as
a follow-up — needs cross-client identification logic.

Test plan

• bats tests/check-update.bats — 10/10 still passing
  (script-level TELEMETRY emission unchanged)
• Manual end-to-end: directly invoke
  agentkey_internal({path: "telemetry/event", params: {event: "upgrade_decision", properties: {...}}})
  → confirmed all fields land in PostHog
• Smoke after release: bump version, install fresh, trigger a real
  upgrade flow, verify PostHog receives populated skill_loaded /
  upgrade_decision / upgrade_result

🤖 Generated with Claude Code