Build and tools

• Normal build: aurac is built with the project and runs before the target.
• Cross-builds (embedded): aurac must run on the build machine. Build it natively once and pass it with -DAURAC_EXECUTABLE=/path/aurac. libs/aura-lang has no dependencies for this purpose.
• Errors in an .aura file stop the build with file:line:column: error: ..., for example an unknown property, unknown ID, ID used before its definition, incorrect type, unknown field, unknown signal, or duplicate type or file name. Missing theme values are reported by the C++ compiler, also with the .aura line thanks to #line.
• #line: the code for each property, each repeat list, and each if condition is preceded by #line <line> "<file.aura>", followed by a #line returning to the generated file. Compiler errors, backtraces, and the debugger therefore point to the .aura line; in gdb, break abort.aura:10 works. The column in compiler messages still refers to the generated code. To debug the generated C++, disable this with -DAURA_LINE_DIRECTIVES=OFF (CMake) or aurac --no-line.
• VS Code: tools/aura-vscode provides highlighting, formatting, completion (properties for each element type, components across the entire UI tree, place directives, IDs, theme values), error checking while typing (aurac --check, without a running preview), and live preview. Installation and tests: tools/aura-vscode/README.md. After changing schema.h, run node tools/aura-vscode/scripts/generate.js.