docs: add agent guidance files and templates

CLAUDE.md

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+# Claude Instructions
+
+## Working style
+
+- Prefer small, focused changes.
+- Do not refactor unrelated code.
+- Do not change public behavior outside the task scope.
+- For non-trivial tasks, plan before editing.
+- If no code change is needed, stop and explain why with evidence.
+- If requirements are ambiguous, list assumptions and choose the safest minimal default.
+- Keep generated artifacts in `.agent/tasks/<task-id>/` when the task is medium or larger.
+
+## Task lanes
+
+Use the smallest lane that fits the work.
+
+### Fast lane
+Use for obvious one-file changes, typos, small logging changes, or simple renames.
+
+Workflow:
+1. Implement directly.
+2. Run the smallest relevant verification.
+3. Show the diff.
+
+### Standard lane
+Use for most product changes and bugs.
+
+Workflow:
+1. Explore relevant code.
+2. Produce a concise plan.
+3. Wait for approval before editing.
+4. Implement the approved plan.
+5. Run verification.
+6. Review the diff.
+7. Fix only accepted blockers/warnings.
+
+### Cautious lane
+Use for authentication, authorization, billing, payments, user data, migrations, concurrency, infrastructure, or broad refactors.
+
+Workflow:
+1. Create or update `.agent/tasks/<task-id>/brief.md`.
+2. Explore read-only.
+3. Produce a plan.
+4. Review the plan adversarially before editing.
+5. Implement in small steps.
+6. Run all relevant verification.
+7. Review the diff in a fresh context.
+8. Fix only accepted blockers/warnings.
+
+## Verification
+
+Before considering a task complete, run relevant project checks. Prefer commands declared by the project, such as:
+
+- test command
+- lint command
+- typecheck command
+- build command
+
+If a command is unavailable, say so explicitly. Never claim a command passed unless it was run in this session and its output was inspected.
+
+## Planning output
+
+For non-trivial tasks, produce a plan with:
+
+- task classification: Fast, Standard, or Cautious;
+- 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.
+
+Wait for approval before editing.
+
+## Review policy
+
+Before finalizing Standard or Cautious tasks, review the diff against the task brief and approved plan.
+
+Report real issues only:
+
+- bugs;
+- missing requirements;
+- missing tests;
+- regressions;
+- security risks;
+- data consistency risks;
+- concurrency/idempotency risks;
+- out-of-scope changes.
+
+Avoid subjective style comments unless they affect correctness or maintainability.
+
+## Git
+
+- Work on a dedicated branch for non-trivial tasks.
+- Keep commits focused.
+- Show `git diff` before committing.
+- Never force push unless explicitly instructed.
+- Do not commit secrets, `.env` files, local databases, logs, or generated dependency folders.