chore: add Codex and agent workflow foundation

.agents/skills/task-closeout/SKILLS.md

@@ -0,0 +1,20 @@
+---
+name: task-closeout
+description: Use this skill when a development task is complete and needs a clean closeout: commit, docs check, merge target confirmation, and summary.
+---
+
+When this skill is used:
+
+1. Verify the current branch is a task branch, not main or develop.
+2. Verify the task scope was respected.
+3. Check whether docs or tests need updates.
+4. Prepare a clean commit message.
+5. Confirm the intended merge target.
+6. Summarize:
+   - what changed
+   - what was not changed
+   - what remains open
+7. Stop.
+
+Do not perform release actions.
+Do not merge into main.