Add REPO_POLICIES.md, rename CLAUDE.md to AGENTS.md, deduplicate (#51)

Closes #48

## Changes

- **Added `REPO_POLICIES.md`** — copied from the standard template at [sneak/prompts](https://git.eeqj.de/sneak/prompts/src/branch/main/prompts/REPO_POLICIES.md) (last_modified: 2026-03-10). This is the authoritative cross-project policy document covering repository structure, tooling, Docker, formatting, testing, and workflow standards.

- **Renamed `CLAUDE.md` → `AGENTS.md`** — deduplicated content:
  - Rules already covered by `REPO_POLICIES.md` (e.g. `git add -A`, Makefile targets) are no longer repeated
  - `AGENTS.md` retains only agent-specific workflow instructions: test-first bug fixing, no AI attribution in commits, per-change make fmt/test/lint workflow, and repo-specific notes (proto files, FORMAT.md, TODO.md)

- **Updated `README.md`** — added a reference to `REPO_POLICIES.md` in the Participation section

- **Formatting** — `make fmt` (prettier) applied to all markdown files

## Verification

`docker build .` passes clean — lint, fmt-check, and all tests green.

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #51
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

AGENTS.md

@@ -0,0 +1,29 @@
+# Agent Instructions
+
+Read `REPO_POLICIES.md` before making any changes. It is the authoritative
+source for coding standards, formatting, linting, and workflow rules.
+
+## Workflow
+
+- When fixing a bug, write a failing test FIRST. Only after the test fails,
+  write the code to fix the bug. Then ensure the test passes. Leave the test in
+  place and commit it with the bugfix. Don't run shell commands to test bugfixes
+  or reproduce bugs. Write tests!
+
+- After each change, run `make fmt`, then `make test`, then `make lint`. Fix any
+  failures before committing.
+
+- After each change, commit only the files you've changed. Push after committing.
+
+## Attribution
+
+- Never mention Claude, Anthropic, or any AI/LLM tooling in commit messages. Do
+  not use attribution.
+
+## Repository-Specific Notes
+
+- This is a Go library + CLI tool for generating `.mf` manifest files.
+- The proto definition is in `mfer/mf.proto`; generated `.pb.go` files are
+  committed (required for `go get` compatibility).
+- The format specification is in `FORMAT.md`.
+- See `TODO.md` for the 1.0 implementation plan and open design questions.