docs: add agent guidance files and templates

.claude/skills/fix-review/SKILL.md

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+---
+description: Fix only accepted findings from a diff review. Use after review-diff returns blockers or warnings that the user accepts.
+disable-model-invocation: true
+---
+
+Fix only the accepted review findings.
+
+Rules:
+
+- Do not rewrite the solution.
+- Do not expand scope.
+- Do not address subjective style comments unless accepted by the user.
+- Preserve the original plan unless the user explicitly approved a change.
+- Add or update tests only when needed to cover the accepted finding.
+- Run relevant verification commands again.
+
+Final report:
+
+## Fixes applied
+
+## Files changed since review
+
+## Commands run
+
+## Remaining risks

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

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+---
+description: Implement an approved plan with minimal scope, tests, and verification. Use after the user approves a plan.
+disable-model-invocation: true
+---
+
+Implement the approved plan.
+
+Rules:
+
+- Follow the approved plan exactly.
+- Keep the diff minimal.
+- Do not refactor unrelated code.
+- Do not change behavior outside the task scope.
+- Add or update tests for changed behavior.
+- Run the verification commands from the plan or task brief.
+- Fix failures caused by your changes.
+- Stop and explain before expanding scope.
+- If a verification command is unavailable, explain why.
+
+Final report:
+
+## Summary
+
+## Files changed
+
+## Tests added or updated
+
+## Commands run
+
+## Remaining risks

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

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+---
+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.

.claude/skills/review-diff/SKILL.md

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+---
+description: Review the current git diff against the task brief and approved plan in a fresh read-only context. Use before finalizing Standard or Cautious tasks.
+disable-model-invocation: true
+context: fork
+disallowed-tools: Write Edit MultiEdit
+---
+
+Review the current diff against the task brief and approved plan.
+
+Use the live git state below as the source of truth.
+
+## Current branch
+
+!`git branch --show-current || true`
+
+## Git status
+
+!`git status --short || true`
+
+## Diff stat
+
+!`git diff --stat HEAD || true`
+
+## Diff
+
+!`git diff HEAD || true`
+
+## Instructions
+
+Look for:
+
+- missing requirements;
+- bugs;
+- missing edge cases;
+- missing tests;
+- regressions;
+- security risks;
+- data consistency risks;
+- concurrency or idempotency risks;
+- unrelated changes.
+
+Do not comment on subjective style preferences unless they affect correctness or maintainability.
+
+Return exactly:
+
+## Blockers
+
+## Warnings
+
+## Suggested tests
+
+## Out-of-scope changes
+
+## Verdict
+
+Use `approve` or `request changes` for the verdict.