pkg: wire top-level CMake, clang-format/tidy, editorconfig

CMakeLists.txt: every lane's add_subdirectory() is now guarded by EXISTS
on that lane's CMakeLists.txt, so main configures no matter which lanes
have merged and a lane lights up its targets on merge with no edit here.
Dependencies are found at top level (gated on the consuming lane) so a
missing -dev package fails fast with a clear name. Warnings via
add_compile_options (survives the presets' CMAKE_CXX_FLAGS override);
VELOX_WERROR escape hatch. Verified end to end: `cmake --preset dev`
against a merged lane/core builds libveloxcore + tests, `ctest --preset
dev` green.

.clang-format: Google base, 4-space indent, 100 cols, right-aligned
pointers. .clang-tidy: small high-signal set (bugprone/performance/
concurrency/portability + selected modernize/readability). .editorconfig
mirrors both. .gitignore: build-*/ , CMakeUserPresets.json, profiling
and editor droppings.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HPPSGhiArbvQgwC2DNiURS

.gitignore

@@ -1,15 +1,39 @@
+# Build output
 build/
-.cache/
+build-*/
+/out/
 compile_commands.json
+CMakeUserPresets.json
+.cache/
+.ccls-cache/
+
+# Language / tooling
 node_modules/
 dist/
 web-ext-artifacts/
+.venv/
+__pycache__/
+*.pyc
+
+# Compiled objects
 *.o
 *.so
 *.a
-*.log
-.venv/
-__pycache__/
+
+# Editor / OS
+.idea/
+.vscode/
+*.user
+*.orig
+*.swp
 .DS_Store
+
+# Profiling
+perf.data*
+callgrind.out.*
+massif.out.*
+
+# Runtime / logs / partial downloads
+*.log
 *.veloxpart
 *.veloxpart.meta