refactor!: remove Zig implementation

BREAKING CHANGE: Remove all Zig source files in preparation for TypeScript rewrite.

Removed files:
- build.zig (Zig build system)
- src/main.zig, src/cli.zig, src/config.zig
- src/loop.zig, src/executor.zig, src/evaluator.zig
- src/plan.zig, src/state.zig, src/ideas.zig
- src/logger.zig, src/fs.zig, src/validate.zig

Signed-off-by: leocavalcante <[email protected]>

Author: leocavalcante