feat: Rust rewrite scaffolding with embedded kustomize+helm

Phase 0 of Python-to-Rust CLI rewrite:

- Cargo.toml with all dependencies (kube-rs, reqwest, russh, rcgen, lettre, etc.)
- build.rs: downloads kustomize v5.8.1 + helm v4.1.0 at compile time, embeds as bytes, sets SUNBEAM_COMMIT from git
- src/main.rs: tokio main with anyhow error formatting
- src/cli.rs: full clap derive struct tree matching all Python argparse subcommands
- src/config.rs: SunbeamConfig serde struct, load/save ~/.sunbeam.json
- src/output.rs: step/ok/warn/table with exact Python format strings
- src/tools.rs: embedded kustomize+helm extraction to cache dir
- src/kube.rs: parse_target, domain_replace, context management
- src/manifests.rs: filter_by_namespace with full test coverage
- Stub modules for all remaining features (cluster, secrets, images, services, checks, gitea, users, update)

23 tests pass, cargo check clean.

src/output.rs

@@ -0,0 +1,92 @@
+/// Print a step header.
+pub fn step(msg: &str) {
+    println!("\n==> {msg}");
+}
+
+/// Print a success/info line.
+pub fn ok(msg: &str) {
+    println!("    {msg}");
+}
+
+/// Print a warning to stderr.
+pub fn warn(msg: &str) {
+    eprintln!("    WARN: {msg}");
+}
+
+/// Return an aligned text table. Columns padded to max width.
+pub fn table(rows: &[Vec<String>], headers: &[&str]) -> String {
+    if headers.is_empty() {
+        return String::new();
+    }
+
+    let mut col_widths: Vec<usize> = headers.iter().map(|h| h.len()).collect();
+    for row in rows {
+        for (i, cell) in row.iter().enumerate() {
+            if i < col_widths.len() {
+                col_widths[i] = col_widths[i].max(cell.len());
+            }
+        }
+    }
+
+    let header_line: String = headers
+        .iter()
+        .enumerate()
+        .map(|(i, h)| format!("{:<width$}", h, width = col_widths[i]))
+        .collect::<Vec<_>>()
+        .join("  ");
+
+    let separator: String = col_widths
+        .iter()
+        .map(|&w| "-".repeat(w))
+        .collect::<Vec<_>>()
+        .join("  ");
+
+    let mut lines = vec![header_line, separator];
+
+    for row in rows {
+        let cells: Vec<String> = (0..headers.len())
+            .map(|i| {
+                let val = row.get(i).map(|s| s.as_str()).unwrap_or("");
+                format!("{:<width$}", val, width = col_widths[i])
+            })
+            .collect();
+        lines.push(cells.join("  "));
+    }
+
+    lines.join("\n")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_table_basic() {
+        let rows = vec![
+            vec!["abc".to_string(), "def".to_string()],
+            vec!["x".to_string(), "longer".to_string()],
+        ];
+        let result = table(&rows, &["Col1", "Col2"]);
+        assert!(result.contains("Col1"));
+        assert!(result.contains("Col2"));
+        assert!(result.contains("abc"));
+        assert!(result.contains("longer"));
+    }
+
+    #[test]
+    fn test_table_empty_headers() {
+        let result = table(&[], &[]);
+        assert!(result.is_empty());
+    }
+
+    #[test]
+    fn test_table_column_widths() {
+        let rows = vec![vec!["short".to_string(), "x".to_string()]];
+        let result = table(&rows, &["LongHeader", "H2"]);
+        // Header should set minimum width
+        for line in result.lines().skip(2) {
+            // Data row: "short" should be padded to "LongHeader" width
+            assert!(line.starts_with("short     "));
+        }
+    }
+}