CI: Add Instructions for GitHub Copilot

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

.github/copilot-instructions.md

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+# Instructions for GitHub Copilot
+
+## Purpose
+
+- Provide Copilot with the single sources of truth for building, testing, and contributing to PhotoPrism.
+- Improve PR reviews and code suggestions by aligning them with our documented workflows and style.
+
+## Single Sources of Truth (SOT)
+
+- Makefile targets (always prefer existing 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 (Swagger): https://docs.photoprism.dev/
+- REST API Guide: https://docs.photoprism.app/developer-guide/api/
+- Agents reference for tools/commands: https://github.com/photoprism/photoprism/blob/develop/AGENTS.md
+
+## Build & Run (local dev; use Makefile first)
+
+- Show tasks: `make help`
+- Build local image: `make docker-build`
+- Start dev env: `docker compose up` (add `-d` for detached)
+- Logs: `docker compose logs -f --tail=100 photoprism`
+- Open app: http://localhost:2342/  (HTTP)  /  https://app.localssl.dev/  (TLS via Traefik when enabled)
+- From the dev container:
+  - Install deps: `make dep`
+  - Build frontend: `make build-js` (or `cd frontend && npm run build`)
+  - Build backend: `make build-go`
+  - Watch frontend: `make watch-js` (stop with Ctrl+C)
+  - Run server binary: `./photoprism start`
+
+## Tests & Lint
+
+- Full tests: `make test`
+- Frontend tests (Vitest): `make test-js` (watch: `make vitest-watch`, coverage: `make vitest-coverage`)
+- Backend tests: `make test-go`
+- Formatting:
+  - Go: `go fmt`, `goimports` (see `make fmt`, `make fmt-go`)
+  - JS/Vue: use scripts in `frontend/package.json` (ESLint + Prettier)
+
+## Project Structure & Languages
+
+- Backend: Go (`internal/`, `pkg/`, `cmd/`) + MariaDB/SQLite
+- Frontend: Vue 3 + Vuetify 3 (`frontend/`)
+- Docker/compose for dev/CI; Traefik used for local TLS in dev profile when enabled.
+
+## Code Review Instructions (for Copilot)
+
+- Respect SOT above; do not invent flags, env vars, or Compose options. If a command/env var is not in the docs/Makefile/CLI help, say “not documented” and suggest checking the SOT.
+- Prefer minimal, surgical diffs. Propose changes as concrete patches and reference the relevant Makefile target or doc section.
+- Before suggesting refactors, check tests and build tasks exist and can pass with the change. If tests are missing, suggest specific Vitest/Go test snippets.
+- Security: never suggest committing secrets; prefer env vars and `.env` in dev only. Point to SECURITY.md for disclosures.
+- Data safety: never run or recommend destructive CLI operations in examples without explicit backups and `--yes`. Avoid `photoprism reset`, `photoprism users reset`, `photoprism auth reset`, or `photoprism audit reset` in PR comments unless the change is specifically about those commands; if unavoidable, add bold warnings and backup steps.
+- Database/schema: if a change touches persistence, check for migrations and mention `photoprism migrate` / `migrations` commands.
+- API changes: align with the REST API docs/spec; include curl examples only if they match current endpoints and auth notes.
+- UX/i18n: keep UI strings concise, translatable, and consistent; avoid hard-coded language constructs; prefer existing patterns/components.
+
+## Style & Patterns
+
+- Go: idiomatic Go, clear error handling, small functions, packages with focused responsibilities. Keep public surface minimal. Add/adjust unit tests.
+- Vue/JS: options API, store patterns as in existing code, avoid breaking translations. Keep ESLint/Prettier clean.
+- Config & flags: suggest `photoprism --help`, `photoprism show config-options` or `photoprism show config-yaml` to verify names before using them.
+
+## Performance & Reliability
+
+- Prefer using existing caches, workers, and batching strategies referenced in code and Makefile. Consider memory/CPU impact; suggest benchmarks or profiling only when justified.
+
+## When Unsure
+
+- Ask for the exact Makefile target or doc link you need, then proceed. Defer to SOT if any conflict arises.
+
+## References To Help Copilot Answer Questions
+
+- Show supported formats/filters: run `photoprism show file-formats` and `photoprism show search-filters` (use results rather than guessing).
+- For CI/dev containers, assume Linux/Unix shell by default; link Windows specifics in Developer Guide FAQ.
+
+## Output Expectations
+
+- Prefer short, actionable comments with code blocks that pass tests locally: `make test-js` (frontend) / `make test-go` (backend)
+- If a suggestion requires additional context (e.g., DB access, external service), call it out explicitly.
+
+## Safety Checklist Before Proposing a CLI Command
+
+- Include a dry-run or non-destructive variant if possible.
+- Recommend creating/using backups before any reset/migrate.

.github/instructions/backend.instructions.md

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+---
+applyTo:
+- "internal/**"
+- "pkg/**"
+- "cmd/**"
+---
+
+For backend changes:
+
+- Maintain Go style; keep functions small, errors wrapped with context.
+- Add/update unit tests; ensure `make test-go` passes.
+- Touching schema? Mention migrations and verify with `photoprism migrations ls`/`migrate`.
+- For CLI/config, confirm flags/envs via `photoprism --help` / `photoprism show config-options` before suggesting.

.github/instructions/frontend.instructions.md

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+---
+applyTo:
+- "frontend/**"
+---
+
+For frontend changes:
+
+- Keep Vue 3 idioms; prefer options API and existing components.
+- Run `make build-js` and `make test-js`; fix ESLint/Prettier before proposing changes.
+- Avoid introducing global state; follow existing store patterns.
+- Keep strings translatable; don’t hardcode locales.
+- For performance, avoid unnecessary reactivity and re-renders; justify new deps.