fix: skip noon pose image when engine starts after noon

[MateoLostanlen]

• Engine used to send the daily pose image immediately at startup whenever it booted after 12:00, since last_pose_image_sent was None and the now >= today_noon branch fired on the first inference call.
• Some stations reboot every night, so on next-day startup they would capture and upload a dark/empty night-time pose image — useless data.
• Anchor last_pose_image_sent at engine construction so the schedule only fires on a real noon crossing during the run; next noon after startup is the first send.
• Adds tests for startup-after-noon, noon crossing, and next-day noon.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.89%. Comparing base (15dd831) to head (6064181).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #365      +/-   ##
===========================================
+ Coverage    72.74%   73.89%   +1.15%     
===========================================
  Files            6        6              
  Lines          631      632       +1     
===========================================
+ Hits           459      467       +8     
+ Misses         172      165       -7     

Flag	Coverage Δ
unittests	73.89% <100.00%> (+1.15%)	⬆️

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