feat: add click-based colorized output with progress events and build timer

- Add click as explicit dependency (already bundled with typer)
- Replace typer.echo calls with click.echo + click.style for colorized output
- Add BuildEvent enum and ProgressCallback to builder for decoupled progress reporting
- Remove direct typer dependency from builder module
- Show per-target status with colored labels (skip/ok/fail/...)
- Display elapsed build time in summary
- Colorize graph and clean command output
- Update CLI tests to match new output format

uv.lock

@@ -49,6 +49,7 @@ name = "bulkgen"
 version = "0.1.0"
 source = { editable = "." }
 dependencies = [
+    { name = "click" },
     { name = "httpx" },
     { name = "mistralai" },
     { name = "networkx" },
@@ -67,6 +68,7 @@ dev = [
 
 [package.metadata]
 requires-dist = [
+    { name = "click", specifier = ">=8.0.0" },
     { name = "httpx", specifier = ">=0.27.0" },
     { name = "mistralai", specifier = ">=1.0.0" },
     { name = "networkx", specifier = ">=3.6.1" },