build: live view for source builds, pin LC_ALL for the pipeline

Route 'pkh build' through the DebUi capture machinery 'pkh deb'
already uses instead of letting dpkg-source inherit the terminal:

- pin LANG=C and LC_ALL=C so dpkg-source emits deterministic English
  diagnostics regardless of the session locale;
- new DpkgSourceClassifier rewrites info:/warning:/error: lines into
  colored pane entries, telling benign tar warnings from failures;
- DebUi generalizes for reuse (arbitrary phase labels, build-specific
  log naming); run_source_build() drives phases and pipes subprocess
  output through the sink when a UI is present;
- glyph-free house-style summaries: 'Built in Ns:' plus artifact
  paths relative to cwd; failures print captured errors + log path;
- drop/capitalize pipeline chatter, add 'pkh build --verbose' to
  bypass the view like 'pkh deb --verbose'.

src/main.rs

@@ -58,7 +58,11 @@ fn main() {
                 .arg(arg!(--backport "This changelog is for a backport entry").required(false))
                 .arg(arg!(-v --version <version> "Target version").required(false)),
         )
-        .subcommand(Command::new("build").about("Build the source package (into a .dsc)"))
+        .subcommand(
+            Command::new("build")
+                .about("Build the source package (into a .dsc)")
+                .arg(arg!(--verbose "Show raw tool output instead of the live build view").required(false)),
+        )
         .subcommand(
             Command::new("deb")
                 .about("Build the source package into binary package (.deb)")
@@ -248,9 +252,22 @@ fn main() {
                     std::process::exit(1);
                 });
         }
-        Some(("build", _sub_matches)) => {
+        Some(("build", sub_matches)) => {
             let cwd = current_dir_or_exit();
-            if let Err(e) = pkh::build::build_source_package(Some(&cwd)) {
+            let verbose = sub_matches
+                .get_one::<bool>("verbose")
+                .copied()
+                .unwrap_or(false);
+
+            // Live build view: disabled by --verbose or when stdout is not a
+            // terminal (DebUi handles the non-TTY case itself)
+            let ui = if verbose {
+                None
+            } else {
+                Some(std::sync::Arc::new(pkh::ui::deb::DebUi::new(&multi)))
+            };
+
+            if let Err(e) = pkh::build::build_source_package(Some(&cwd), ui) {
                 error!("{}", e);
                 // Unmet build dependencies/conflicts exit with status 3,
                 // like dpkg-buildpackage does.