Add AGENTS.md and CLAUDE.md

AGENTS.md

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+# AGENTS GUIDANCE
+
+This file provides guidance to AI agents when working with code in this repository.
+
+## Build
+
+Out-of-source builds are required. In-source builds will be rejected by CMake.
+
+```bash
+cmake -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build --parallel
+```
+
+Build options:
+- `DECOMPRESSION_BACKEND`: `unarr` | `7zip` | `libarchive` (default: 7zip on Windows/macOS, unarr on Linux)
+- `PDF_BACKEND`: `pdfium` | `poppler` | `pdfkit` | `no_pdf` (default: pdfium on Windows, pdfkit on macOS, poppler on Linux)
+- `BUILD_SERVER_STANDALONE=ON`: builds only `YACReaderLibraryServer` (headless), requires only Qt 6.4+
+- `BUILD_TESTS=ON` (default): enables the test suite
+
+## Tests
+
+```bash
+ctest --test-dir build --output-on-failure
+```
+
+Tests live in `tests/` and are built as Qt Test executables (`compressed_archive_test`, `concurrent_queue_test`).
+
+## Code Formatting
+
+CI enforces `clang-format`. Run it before committing. There are multiple `.clang-format` files — subdirectories for third-party code have their own to opt out of reformatting. Always run recursively from the repo root via the provided scripts:
+
+- Linux: `scripts/clang-format-linux.sh`
+- macOS: `scripts/clang-format-macos.sh`
+- Windows: `scripts\clang-format-windows.cmd` (or `.ps1`)
+
+Style is WebKit-based with custom brace wrapping (braces on same line for control flow, new line after functions/classes), no column limit, and `SortIncludes: false`.
+
+## Architecture
+
+The repo builds three applications that share a common set of static libraries:
+
+| App | Description |
+|-----|-------------|
+| `YACReader` | Comic viewer |
+| `YACReaderLibrary` | Comic library manager (GUI) |
+| `YACReaderLibraryServer` | Headless HTTP server |
+
+### Static library dependency layers (bottom to top)
+
+1. **`yr_global`** — version/global constants, no GUI, used by everything
+2. **`naturalsort`, `concurrent_queue`, `worker`** — utilities
+3. **`common_all`** — shared non-GUI: `ComicDB`, `Folder`, `Bookmarks`, HTTP helpers, cover utils
+4. **`comic_backend`** — comic file abstraction + PDF backend (source varies by `PDF_BACKEND`)
+5. **`cbx_backend`** — compressed archive abstraction (in `compressed_archive/`)
+6. **`db_helper`** — SQLite database layer: schema management, reading lists, query parser
+7. **`library_common`** — library scanning, bundle creation, XML metadata parsing; shared between `YACReaderLibrary` and `YACReaderLibraryServer`
+8. **`common_gui`** — GUI widgets, themes infrastructure, version check (not built in `BUILD_SERVER_STANDALONE`)
+9. **`rhi_flow_reader` / `rhi_flow_library`** — RHI-based 3D coverflow widget, compiled twice with different defines (`YACREADER` vs `YACREADER_LIBRARY`); shaders compiled via `qt_add_shaders()`
+
+### Key design notes
+
+- **Theme system**: `theme_manager.h/cpp` is NOT part of `common_gui` because it depends on app-specific `Theme` structs. Each app (`YACReader/themes/`, `YACReaderLibrary/themes/`) defines its own `theme.h` and includes `theme_manager` directly.
+- **Compile-time app identity**: `YACREADER` or `YACREADER_LIBRARY` defines distinguish shared source compiled into different apps.
+- **PDF backend**: resolved at configure time into an `INTERFACE` target `pdf_backend_iface` (see `cmake/PdfBackend.cmake`); `comic_backend` and `common_all` link against this interface.
+- **Third-party code**: `third_party/` contains QsLog, KDToolBox, QtWebApp, QrCode — each has its own `.clang-format` to prevent reformatting.
+- **Runtime dependencies**: Qt binaries must be in `PATH`; third-party DLLs/dylibs must be next to the executable. Check an existing YACReader installation for the required files.
+
+### PRs
+
+Target branch is always `develop`.