Add README, task format docs, fix archived memos API

- README.md: introduction, features, build/install, tech stack,
  disclaimer, acknowledgements, logo at top
- TASK_FORMAT.md: full task syntax reference with examples,
  validation rules, typo detection, notification behavior
- Fix archived memos: use state query param instead of CEL filter
- LOGO.md: remove triangle variant, keep circle only
- logo-circle.svg tracked for README rendering

Signed-off-by: Avinal Kumar <avinal.xlvii@gmail.com>
Co-Authored-By: Claude Opus 4.6 (1M context)

.gitignore

@@ -29,4 +29,4 @@ styles.css
 # Dev artifacts
 PLAN.md
 Screenshot_*.png
-logo-*.svg
+logo-triangle.svg