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

.clang-format

@@ -0,0 +1,29 @@
+# Velox C++ style. Owned by lane PKG/QA; CLAUDE.md §6 makes this authoritative.
+# `clang-format --dry-run -Werror` runs on every PR.
+---
+Language: Cpp
+BasedOnStyle: Google
+
+IndentWidth: 4
+ContinuationIndentWidth: 4
+ColumnLimit: 100
+AccessModifierOffset: -2
+NamespaceIndentation: None
+
+DerivePointerAlignment: false
+PointerAlignment: Right
+
+AllowShortFunctionsOnASingleLine: Inline
+AllowShortIfStatementsOnASingleLine: Never
+AllowShortLoopsOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+
+IndentCaseLabels: true
+
+IncludeBlocks: Preserve
+SortIncludes: CaseSensitive
+
+# Keep the "}  // namespace vdm" trailer style Google uses.
+FixNamespaceComments: true
+ShortNamespaceLines: 0
+---