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/ui.rs

@@ -13,8 +13,27 @@ use crossterm::{
 };
 use indicatif::{MultiProgress, ProgressBar, ProgressStyle};
 use std::io::{self, Write};
+use std::path::Path;
 use std::time::Duration;
 
+/// Render a path for terminal display: relative to the current working
+/// directory when the target lives inside it or directly next to it
+/// (`../name`, the usual layout of build artifacts), absolute otherwise.
+pub fn display_path(path: &Path) -> String {
+    let Ok(cwd) = std::env::current_dir() else {
+        return path.display().to_string();
+    };
+    if let Ok(rel) = path.strip_prefix(&cwd) {
+        return rel.display().to_string();
+    }
+    if let Some(parent) = cwd.parent()
+        && let Ok(rel) = path.strip_prefix(parent)
+    {
+        return format!("../{}", rel.display());
+    }
+    path.display().to_string()
+}
+
 /// Create a spinner-style progress bar attached to `multi`, returning the bar
 /// and a callback compatible with [`crate::ProgressCallback`]
 pub fn create_progress_bar(