Add weeknotes system with /weeknotes command

- Create weeknotes archetype for manual post creation
- Add /weeknotes slash command that prompts through each section
  interactively (shipped, read, played, cooked, noticed, thinking, next)
- Add /weeknotes landing page explaining the concept
- Update CLAUDE.md with weeknotes documentation and voice guidelines

Weeknotes are brief weekly reflections—lighter than full posts, more
personal journal than polished article.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

content/weeknotes.md

@@ -0,0 +1,11 @@
+---
+title: Weeknotes
+aliases:
+  - /weeknotes/
+---
+
+Weeknotes are short, personal reflections on the week—what I shipped, read, played, cooked, noticed, and thought about. They're a way to mark time and notice patterns.
+
+The format comes from the [weeknotes movement](https://indieweb.org/weeknotes), which grew out of the UK digital government community and spread through personal blogs. [Giles Turnbull's guide](https://doingweeknotes.com/) and [Tracy Durnell's reflections](https://tracydurnell.com/2024/07/30/using-personal-weeknotes-as-a-tool-for-attention/) shaped my approach.
+
+Browse all weeknotes: [/tags/weeknotes](/tags/weeknotes/)