Adds a macOS post-build step to patch CEF’s keychain service string to a Nebula-specific name, then re-sign the modified framework (with configurable signing identity or ad-hoc). Also enables Chromium’s `use-mock-keychain` switch on Apple builds to prevent repeated local keychain prompts, fixes titlebar traffic-light hit testing in the mac window view, scopes a WM_CLOSE guard to Windows only, and updates `.clangd` to ignore non-mac platform sources during macOS development.
Introduce a macOS Cocoa-based UI and CEF helper subprocess support. CMake: enable OBJCXX on Apple, treat mac sources as .mm, set -fobjc-arc, link Cocoa frameworks, and generate helper app targets using a mac Info.plist template; keep libcef logical target off macOS. Implementation: add Objective-C++ implementations for browser_host and nebula_window, convert startup to ObjC++ (prepare NSApplication), add process_helper_mac (CEF helper entry) and load CEF library from main/main_bigpicture on mac. Tooling/docs: add .clangd fallback flags, compile_commands symlink helper, update cross-platform docs for mac status. Misc: add menu-popup UI page, define UNREFERENCED_PARAMETER in platform/types.h, small code cleanups (use (void)layout, include platform/types.h) and update .gitignore.
andrew