docs: trim README, extract architecture notes to docs/ARCHITECTURE.md
README went from 1094 to 671 lines (-39%) by removing:
- "Technical Deep Dive" section (had stale NTPState enum showing removed values;
useful content moved to docs/ARCHITECTURE.md)
- "The Journey: v1.7 → v1.9.8" — ~250 lines duplicating CHANGELOG;
replaced with one-paragraph summary and CHANGELOG link
- "Memory Evolution" table — already in CHANGELOG entries
- "What's Next: Home Assistant Integration" — year-old vaporware promise
- "Lessons Learned" section — editorial blog filler
- "Final Thoughts" + "P.S." footer — same
Added docs/ARCHITECTURE.md (~110 lines) with the useful technical content:
async model, timer correctness, memory budget, IRAM discipline,
heap fragmentation pattern, EEPROM layout, factory reset, web server.
TOC restructured into "Story" (history) and "Use it" (practical) sections.
Alex Petrochenko
75b6a21f3c