[Sisyphus] phase-2 / zcc / Wave 0 — Scaffold (build.zig + driver entry)

## Scope
Deliver the initial Zig build system and CLI driver entry point for the `zcc` C11 compiler.

## Deliverables
- `phase2/zcc/build.zig` — Zig 0.16 build script, zero external dependencies, produces `zcc` executable.
- `phase2/zcc/src/main.zig` — CLI driver entry point.
- `phase2/zcc/src/cli.zig` — basic CLI argument parsing (`--help`, `-E`, `-o`, `-c`, `-O0`/`-O2`, `-g`, `-fsanitize=...`).

## Success Criteria
1. `zig build` completes without errors on macOS and inside a Linux Docker container.
2. `./zig-out/bin/zcc --help` prints usage and exits 0.
3. `zcc -E foo.c` runs the preprocessor-only stub (lexes and prints tokens to stdout, no codegen).
4. No external Zig package dependencies; only stdlib.

## Dependencies on Prior Waves
- None (Wave 0 is the root).

## Suggested Role Assignment
`scaffold-engineer`

## Test Corpus Expectations
- Unit test: `zig build test` runs `cli.zig` tests (argument parsing edge cases).
- Integration: `zcc --help` and `zcc -E` on a trivial `hello.c` in CI.

Start with the deliverables in phase2/zcc/build.zig, src/main.zig, and src/cli.zig, then review the existing repository layout and Zig version requirements. Run zig build and zig build test before implementing the scaffold. Done means the executable builds on macOS and Linux, --help succeeds, -E processes a trivial hello.c, and CLI tests cover the listed options.

Written by the indexing model from the issue text.