fix hassfest: drop invalid 'homeassistant' manifest key; run validation on main

- manifest.json: remove the 'homeassistant' key (not a valid manifest key;
  the min HA version lives in hacs.json). Verified hassfest-clean locally.
- validate.yml / hassfest.yaml: trigger on push to main (default branch) too,
  not only master, so CI actually runs.

custom_components/adaptive_lighting/manifest.json

@@ -5,7 +5,6 @@
   "config_flow": true,
   "dependencies": ["light"],
   "documentation": "https://github.com/CaseyRo/adaptive-lighting#readme",
-  "homeassistant": "2025.1.0",
   "iot_class": "calculated",
   "issue_tracker": "https://github.com/CaseyRo/adaptive-lighting/issues",
   "requirements": ["ulid-transform"],