Add basic AGENTS.md/CLAUDE.md files

AGENTS.md

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+# addons-server — agent guide
+
+This is the Django backend for addons.mozilla.org (AMO). Everything runs inside Docker.
+
+## Global instructions
+
+- Keep code comments to a strict minimum.
+- Do not remove existing comments unless the surrounding code is being refactored.
+- If you can't find something quickly, it is better to ask than run local searches.
+
+## Workflow
+
+- Discuss the approach before writing code for non-trivial changes, use plan mode.
+- While implementing, run the relevant test suite with `docker compose exec -T web pytest <path to a test file>`.
+- Format code with `make format`.
+
+## Before reporting a change as done
+
+**Mandatory** for every code change, no exceptions. Do not send your closing message without completing this. "Tests pass" and "format ran" are not a substitute — they are two of the items, not the whole list.
+
+Walk through the checklist below against the diff you just produced (not unrelated code), and include the result in your closing message. If an item doesn't apply, say so; if something is a tradeoff you accepted, surface it.
+
+- Scope: changes match what was requested — no unrelated edits, refactors, or cleanup that wasn't asked for.
+- Correctness: the change actually does what it claims. Edge cases and error paths are handled where they matter.
+- Tests: new or changed behavior has test coverage; existing tests still pass. Tests assert behavior, not implementation details.
+- Style: follows surrounding code conventions; no stray debug prints, commented-out blocks, or TODOs left behind.
+- Comments: only present where the why is non-obvious. Remove anything that just restates the code.
+- Dependencies: no new packages added without reason; lockfiles updated if needed.
+- Formatting: `make format` has been run.
+
+This checklist is also the standard to apply when explicitly asked to review code (your own or someone else's).

CLAUDE.md

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+@AGENTS.md