fix(person-follow): fix session leak, tracking spam, and double hook on startup

[Wanbogang]

Summary

#1592

Bug 1 & 2 invalid
Fixes 3 bugs found in person_follow mode affecting stability and LLM token usage.

Changes

Bug 3 — Duplicate lifecycle hook on startup

• Removed start_person_follow_hook from on_startup in config/unitree_go2_modes.json5
• Hook is now only registered under on_entry
• Prevents double enrollment announcement when mode_memory_enabled restores person_follow state on boot

Bug 4 — aiohttp.ClientSession created on every poll

• Added _session instance variable to reuse a single ClientSession across all poll cycles
• Session is recreated automatically if closed
• Prevents socket exhaustion and TCP handshake overhead at 2 polls/second

Bug 5 — TRACKING status messages spammed to LLM

• Added _last_tracking_report throttle — TRACKING updates sent at most every 10 seconds
• State-change events (TRACKING STARTED, SEARCHING, WAITING) bypass throttle and are always sent immediately
• Reduces LLM token usage by ~90% during active tracking

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!