docs: add agent guidance files and templates

.agent/templates/plan.md

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+# Plan
+
+## Task classification
+
+Fast / Standard / Cautious
+
+## Assumptions
+
+- ...
+
+## Files inspected
+
+- `path/to/file`
+
+## Files likely to change
+
+- `path/to/file`
+
+## Files that should not change
+
+- `path/to/file`
+
+## Implementation steps
+
+1. ...
+2. ...
+3. ...
+
+## Tests to add or update
+
+- ...
+
+## Verification commands
+
+- `...`
+
+## Risks and ambiguities
+
+- ...
+
+## Stopping conditions
+
+Stop and ask before continuing if:
+
+- scope needs to expand;
+- existing behavior contradicts the brief;
+- verification cannot be run;
+- a required dependency or secret is missing.

.agent/templates/review.md

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+# Diff Review
+
+## Blockers
+
+- None / ...
+
+## Warnings
+
+- None / ...
+
+## Suggested tests
+
+- None / ...
+
+## Out-of-scope changes
+
+- None / ...
+
+## Verdict
+
+approve / request changes

.agent/templates/task-brief.md

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+# Task Brief
+
+## Task ID
+
+`YYYY-MM-DD-short-name`
+
+## Goal
+
+Describe the intended change in one or two sentences.
+
+## Context
+
+Add links, errors, user stories, examples, existing behavior, or relevant files.
+
+## Non-goals
+
+- Do not ...
+- Do not ...
+
+## Acceptance criteria
+
+- [ ] ...
+- [ ] ...
+- [ ] ...
+
+## Verification
+
+Run the relevant commands for this project:
+
+- `...`
+- `...`
+
+## Risk level
+
+Choose one: Fast / Standard / Cautious
+
+## Notes for Claude
+
+Any constraints, preferred approach, migration concerns, compatibility requirements, or rollout notes.

.agent/templates/verification.md

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+# Verification
+
+## Commands run
+
+- `...`
+
+## Results
+
+- Pass / Fail / Not run
+
+## Failures found
+
+- None / ...
+
+## Fixes applied
+
+- None / ...
+
+## Remaining risks
+
+- None / ...