Develop: Add AGENTS.md file

Provides guidelines and context for coding agents:
- https://agents.md/
- https://agentsmd.net/

Signed-off-by: Michael Mayer <michael@photoprism.app>

.gitignore

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 .c9revisions
 .settings
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-AGENTS.md

AGENTS.md

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+# Repository Guidelines
+
+## Purpose
+
+This file tells automated coding agents (and humans) where to find the single sources of truth for building, testing, and contributing to PhotoPrism. Keep it short to prevent drift.
+
+## Sources of Truth
+
+- Makefile targets: https://github.com/photoprism/photoprism/blob/develop/Makefile
+- Developer Guide (setup): https://docs.photoprism.app/developer-guide/setup/
+- Developer Guide (tests): https://docs.photoprism.app/developer-guide/tests/
+- CONTRIBUTING: https://github.com/photoprism/photoprism/blob/develop/CONTRIBUTING.md
+- SECURITY: https://github.com/photoprism/photoprism/blob/develop/SECURITY.md
+- REST API docs: https://docs.photoprism.dev/
+
+## Build & run (local)
+
+- Run `make help` to see all targets.
+- Install deps: `make dep`
+- Build frontend/backend: `make build-js` and `make build-go`
+- Start locally: run `./photoprism start` from within the Docker container (see below)
+- With Docker/Compose:
+  1. Run `make docker-build` once to build the development environment image based on the `Dockerfile`.
+  2. Run `docker compose up -d` to start the services in `compose.yaml` if they are not already running.
+  3. Run `make terminal` to open a terminal session to the development environment once the services have been started.
+
+## Tests
+
+- Full unit test suite: `make test` (runs backend and frontend from within the development environment)
+- Test frontend/backend: `make test-js` and `make test-go`
+- Frontend unit test scripts are defined in `frontend/package.json`
+- Acceptance tests: use the `acceptance-*` targets in the `Makefile`
+- For more information: https://docs.photoprism.app/developer-guide/tests/
+
+## Code Style & Lint
+
+- Go: `go fmt` / `goimports` (see `Makefile` targets such as `fmt` / `fmt-go`)
+- JS/Vue: use the lint/format scripts in `frontend/package.json` (ESLint + Prettier)
+
+## Safety & Data
+
+- Never commit secrets. Use environment variables or a local `.env`.
+- Do not run destructive commands against production data. Prefer ephemeral volumes and test fixtures when running acceptance tests.
+
+If anything in this file conflicts with the `Makefile` or the Developer Guide, the Makefile and docs win.