Update TODO.md and add task tracking rule to CLAUDE.md

Remove completed/deferred items from TODO.md and add instruction
to use TODO.md as the primary task tracker instead of TodoWrite.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -236,6 +236,15 @@ When adding **new tabs, sections, or major UI elements**, update the correspondi
 - In HTML templates: use `data-i18n="key"` for text content, `data-i18n-title="key"` for title attributes, `data-i18n-aria-label="key"` for aria-labels
 - Keys follow dotted namespace convention: `feature.context.description` (e.g. `device.error.brightness`, `calibration.saved`)
 
+## Task Tracking via TODO.md
+
+Use `TODO.md` in the project root as the primary task tracker. **Do NOT use the TodoWrite tool** — all progress tracking goes through `TODO.md`.
+
+- **When starting a multi-step task**: add sub-steps as `- [ ]` items under the relevant section
+- **When completing a step**: mark it `- [x]` immediately — don't batch updates
+- **When a task is fully done**: mark it `- [x]` and leave it for the user to clean up
+- **When the user requests a new feature/fix**: add it to the appropriate section with a priority tag
+
 ## General Guidelines
 
 - Always test changes before marking as complete