docs: add agent guidance files and templates

.claude/skills/plan-task/SKILL.md

@@ -0,0 +1,37 @@
+---
+description: Plan a coding task before editing. Use for non-trivial implementation, bug fixing, refactoring, or unfamiliar code. Produces a concise plan and waits for approval.
+disable-model-invocation: true
+disallowed-tools: Write Edit MultiEdit
+---
+
+You are planning a coding task.
+
+Read the task brief provided by the user. If a `.agent/tasks/<task-id>/brief.md` file is mentioned, read it first.
+
+Workflow:
+
+1. Explore the relevant code in read-only mode.
+2. Do not edit files.
+3. Classify the task as Fast, Standard, or Cautious.
+4. Produce a concise implementation plan.
+5. Stop and wait for user approval before implementation.
+
+The plan must include:
+
+- task classification;
+- assumptions;
+- files inspected;
+- files likely to change;
+- files that should not change;
+- implementation steps;
+- tests to add or update;
+- verification commands;
+- risks and ambiguities;
+- stopping conditions.
+
+Constraints:
+
+- Keep the scope minimal.
+- Do not refactor unrelated code.
+- Prefer the safest minimal default for ambiguities.
+- If no code change is needed, explain with evidence.