build: modernize repo-lens skeleton and cross-platform configuration

Replace CPM with FetchContent and update GoogleTest to v1.18.0.
Add compiler toolchains and Debug, Release, and sanitizer presets.
Require CMake 4.0, use target properties for compiler settings,
and enable compilation database export.

Fix skeleton compilation errors and adopt trailing return types,
nodiscard execute methods, and noexcept signatures. Update CI
and project documentation without implementing any TODOs.

Validated Windows builds and tests in all three configurations.

docs/PROJECTMAP.md

@@ -0,0 +1,69 @@
+# Project map
+
+This is a routing table: **where should an agent look?** It is not an architecture manual. Start here, then inspect only the source or documentation relevant to the task.
+
+The repository contains a C++ CLI skeleton, native compiler presets, and a sample test. Navigation implementations remain TODOs. The bookmarks below route to existing build invariants, not implemented navigation features.
+
+## Current routes
+
+### Purpose and direction
+Path: `README.md`
+Entry: project purpose, scope, illustrative CLI, and measurement goals.
+Related: `AGENTS.md` for agent operating instructions.
+
+### CLI parsing and dispatch skeleton
+Path: `src/main.cpp`
+Entry: `main`
+Important symbols: `print_usage`, `extract_tool_name`, `extract_tool_arguments`
+Flow: placeholder parsing -> `find`/`map` dispatch -> tool `execute`; parsing and usage remain TODOs.
+Related: `src/CMakeLists.txt` lists all executable sources. `around` has a stub but is not dispatched yet.
+
+### Tool interface and implementations
+Path: `include/repo_tool_*.hpp`, `src/repo_tool_*.cpp`
+Entry: `include/repo_tool_interface.hpp`
+Important symbols: `rl::IRepoLensTool`, `rl::exit_code`, `rl::RepoLensToolFind`, `rl::RepoLensToolMap`, `rl::RepoLensToolAround`
+Related: `AGENTS.md` for trailing return types and the `[[nodiscard]]`/`noexcept` execution contract. Tool bodies remain TODOs.
+Tests: no navigation behavior tests yet.
+
+### Native build and compiler settings
+Path: `CMakeLists.txt`, `CMakePresets.json`, `cmake/`, `src/CMakeLists.txt`
+Entry: `CMakePresets.json` for matching configure/build/test presets; `cmake/toolchains/` for GCC, Clang, AppleClang, and MSVC selection.
+Important symbols: `target_enable_warnings`, `target_warnings_as_errors`, `target_enable_sanitizers`
+Related: `cmake/compilerwarnings.cmake` for diagnostics; `cmake/sanitizers.cmake` for capability checks and target settings; `cmake/staticanalysis.cmake` is an inherited Visual Studio generator helper.
+Bookmarks: `OPTIONAL_TEST_DEPENDENCY_BOUNDARY` in root `CMakeLists.txt` separates the offline application build from test dependencies.
+Ignore normally: generated `build/` and `.build/` trees; build helpers unless the task concerns tooling. Use the selected build's `compile_commands.json` when compilation context is needed.
+
+### Test dependencies and validation
+Path: `test/`, `cmake/gtest.cmake`
+Entry: `test/CMakeLists.txt`; `test/test_main.cpp` is only a sample assertion.
+Flow: `ENABLE_TESTS` -> FetchContent GoogleTest -> `repo-lens-test` -> CTest discovery.
+Bookmarks: `MSVC_SANITIZER_ANNOTATION_ALIGNMENT` in `test/CMakeLists.txt` keeps STL annotations consistent across the instrumented test and its dependencies.
+Related: `<compiler>-sanitizers` presets; `README.md` for local dependency overrides and build instructions.
+
+### CI and formatting
+Path: `.github/workflows/`, `.clang-format`, `.clang-tidy`
+Entry: `.github/workflows/ci.yml` configures/builds/tests Debug, Release, and sanitizer presets on native hosts.
+Related: `.github/workflows/auto-clang-format.yml` is inherited formatting automation; `.clang-tidy` is configuration, not evidence that analysis runs with Ninja.
+Ignore normally: workflows unless the task concerns validation or automation.
+
+## Maintaining the map
+
+Update routes when actual source structure or useful entry points materially change. Add only existing areas; do not predeclare hypothetical subsystems. Keep entries short and omit fields that add no routing value.
+
+Suggested entry shape (fields are optional):
+
+```text
+Subsystem
+Path:
+Entry:
+Important symbols:
+Flow:
+Tests:
+Bookmarks:
+Related:
+Ignore normally:
+```
+
+Use `Flow` for a short sequence of entry points, not an implementation explanation. List bookmarks only for stable semantic or architectural locations where ordinary searchable symbols are insufficient.
+
+Locate bookmark declarations cheaply with `rg -n '@ai-bookmark' CMakeLists.txt test cmake src include`, then inspect a bounded range around the relevant marker. repo-lens bookmark commands are not implemented yet. Prefer symbols for ordinary functions and classes.