feat: add update-docs skill

.claude/skills/update-docs/SKILL.md

@@ -0,0 +1,33 @@
+---
+name: update-docs
+description: Update docs/log with recent session activity
+argument-hint: "[optional focus area]"
+allowed-tools: Bash, Read, Write, Edit, Glob, Grep
+---
+
+# Update Docs
+
+Organize and append recent session activity to `docs/log/`.
+
+## Steps
+
+1. Check existing files in `docs/log/`
+2. Review recent git log and session conversation to summarize work done
+3. Append to the relevant log file. Create a new file if it's a new topic
+
+## File Naming
+
+`NNNN-<slug>.md` (e.g., `0001-initial-setup.md`, `0002-api-tests.md`)
+
+## Writing Rules
+
+- Record what was done, what was decided, and what was discarded
+- Keep it concise. Do not paste code
+- Track completed items with checklists
+
+## Scope
+
+- `docs/log/` — session logs and work records
+- Do not modify `docs/plan/` (plans are managed separately)
+
+Use $ARGUMENTS as additional context for what to focus on.