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/build/env.rs

@@ -12,20 +12,26 @@ pub fn num_parallel() -> usize {
         .unwrap_or(1)
 }
 
-/// Compute the environment variables exported by `dpkg-buildpackage` before
-/// running any build step.
+/// Compute the environment variables exported before running any build step.
 ///
 /// Mirrors dpkg behavior:
 /// - `SOURCE_DATE_EPOCH` from the changelog entry timestamp
 ///   (<https://reproducible-builds.org/specs/source-date-epoch/>),
 /// - `DEB_BUILD_OPTIONS=parallel=N` (auto-detected job count),
 /// - `DEB_BUILD_PROFILES` when non-default profiles are requested.
+///
+/// The locale is pinned to `C` (`LC_ALL`, which takes precedence over any
+/// inherited session setting, plus `LANG`) so build tools emit deterministic,
+/// English diagnostics — required for reliable log classification and
+/// reproducible builds.
 pub fn build_env(
     source_date_epoch: i64,
     parallel: usize,
     build_profiles: &[String],
 ) -> BTreeMap<String, String> {
     let mut env = BTreeMap::new();
+    env.insert("LANG".to_string(), "C".to_string());
+    env.insert("LC_ALL".to_string(), "C".to_string());
     env.insert(
         "SOURCE_DATE_EPOCH".to_string(),
         source_date_epoch.to_string(),
@@ -257,6 +263,8 @@ mod tests {
     #[test]
     fn build_env_values() {
         let env = build_env(1787392800, 16, &[]);
+        assert_eq!(env.get("LANG").unwrap(), "C");
+        assert_eq!(env.get("LC_ALL").unwrap(), "C");
         assert_eq!(env.get("SOURCE_DATE_EPOCH").unwrap(), "1787392800");
         assert_eq!(env.get("DEB_BUILD_OPTIONS").unwrap(), "parallel=16");
         assert!(!env.contains_key("DEB_BUILD_PROFILES"));