chore: add CLAUDE.md for guidance

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build & Test Commands
+
+```bash
+# Build
+./gradlew assembleDebug
+./gradlew assembleRelease          # requires signing env vars
+
+# Unit tests (all flavors)
+./gradlew testDebugUnitTest testMdmDebugUnitTest --continue
+
+# Single module unit tests
+./gradlew :owncloudApp:testOriginalDebugUnitTest
+./gradlew :owncloudData:testDebugUnitTest
+
+# Instrumented tests (requires running emulator/device)
+./gradlew :owncloudData:connectedAndroidTest
+
+# Lint & static analysis
+./gradlew detekt                   # maxIssues: 0 — any issue fails CI
+./gradlew lintDebug
+./gradlew ktlintCheck
+./gradlew ktlintFormat             # auto-fix formatting
+```
+
+## Architecture
+
+Four modules in a strict dependency chain:
+
+```
+owncloudComLibrary → owncloudData → owncloudDomain ← owncloudApp
+```
+
+- **owncloudComLibrary** — networking layer: OkHttp, DAV4Android (WebDAV), OAuth/OIDC, Moshi
+- **owncloudDomain** — business layer: UseCases, domain Models, Repository interfaces, Exceptions
+- **owncloudData** — data layer: Repository implementations, Room DB, Remote/Local DataSources
+- **owncloudApp** — presentation layer: Activities, Fragments, ViewModels, Koin wiring
+- **owncloudTestUtil** — shared test factories, mocks, and extensions (test-only dependency)
+
+**Pattern:** MVVM + Clean Architecture. Data flows strictly in one direction:
+
+```
+Fragment → ViewModel → UseCase → Repository → DataSource → ownCloud server (WebDAV/Graph API)
+```
+
+UseCases extend `BaseUseCase<R>` or `BaseUseCaseWithResult<P, R>`. ViewModels call them via coroutines and expose `Flow` (preferred) or `LiveData` to the UI.
+
+**DI:** Koin with module-per-layer structure under `owncloudApp/.../dependecyinjection/`:
+`CommonModule`, `RemoteDataSourceModule`, `LocalDataSourceModule`, `RepositoryModule`, `UseCaseModule`, `ViewModelModule`.
+
+## Product Flavors
+
+Dimension: `management`
+
+| Flavor | Purpose |
+|--------|---------|
+| `original` | Standard ownCloud app |
+| `mdm` | Mobile Device Management — custom branding/policies |
+| `qa` | QA variant for automated testing |
+
+Build types: `debug` / `release`. Combined targets follow the pattern `assembleOriginalDebug`, `testMdmDebugUnitTest`, etc.
+
+## SDK & Toolchain
+
+- Min SDK 28 (Android 9), Target/Compile SDK 36
+- Kotlin 2.3.10, JDK 17, AGP 9.2.1
+- Version catalog: `gradle/libs.versions.toml`
+
+## Git & Commit Conventions
+
+All commits must be **GPG-signed** and include a **DCO sign-off**:
+
+```bash
+git commit -s -S -m "type: description"
+```
+
+**Conventional Commits** format is enforced by CI:
+- `feat:` introduces a new capability visible to the user or other modules (new screen, new API, new setting)
+- `fix:` corrects a defect — something that was broken and is now working as intended
+- `refactor:` restructuring existing code (rename, extract, move, simplify) with no change to observable behavior
+- `test:` adds or updates tests only — no production code changes
+- `build:` changes to dependencies (adding, removing, or upgrading libraries in `libs.versions.toml` or any `build.gradle`)
+- `chore:` maintenance that has no user-facing effect (changelog entries, build config, tooling) — do not use for dependency changes
+
+Branch naming follows OneFlow: `feature/feature_name`, `fix/fix_name`, `improvement/improvement_name`, `technical/technical_description`.
+
+Rebase on the target branch before opening a PR. No merge commits.
+
+## Changelog
+
+Every PR must include a file in `changelog/unreleased/` named after the PR number (e.g., `4936`):
+
+```
+Enhancement: Short title under 80 chars
+
+Description in present perfect passive tense.
+
+https://github.com/owncloud/android/issues/<issue>  ← optional, omit if there is no linked issue
+https://github.com/owncloud/android/pull/<pr>
+```
+
+Types: `Bugfix`, `Change`, `Enhancement`, `Security`. Calens reads these files to auto-generate `CHANGELOG.md` after merge.
+
+## Key Constraints
+
+- **No translation PRs** — submit translations to Transifex only.
+- **Detekt is zero-tolerance** (`maxIssues: 0`). Run `./gradlew detekt` locally before pushing.
+- **Max line length: 150** (enforced by `.editorconfig`).
+- **GitHub Actions** must use SHA-pinned refs and come from the owncloud org, `actions/*`, or verified Marketplace publishers.
+- **License migration in progress** (GPL-2.0 → Apache 2.0): do not introduce new copyleft dependencies without discussion.
+- **Security issues** go to security.owncloud.com, not GitHub issues.