chore: add Codex and agent workflow foundation

docs/TASK_TEMPLATE.md

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+# Task Template
+
+Use this structure for Codex implementation tasks.
+
+## Required opening
+
+- confirm branch strategy
+- name the branch to use
+- state whether remote update succeeded or local state is being used
+
+## Required execution structure
+
+1. files to change
+2. short design explanation
+3. code/doc/test changes
+4. commit message
+5. merge target
+6. stop
+
+## Constraints
+
+- no work on main
+- no work on develop
+- no history rewrite
+- no broadening scope without approval