fix: detect Unix-style absolute paths on Windows in normalize_relative_path

On Windows, Path::is_absolute() does not recognise Unix-style paths
like /home/user/agents/ctf.md (no drive letter). These were falling
through to the relative path branch and being emitted verbatim, producing
paths like '{{ workspace }}//home/user/agents/ctf.md'.

Add a supplementary starts_with('/') check so these paths are correctly
treated as absolute and fall back to filename-only.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jamesadevine

src/compile/common.rs

@@ -564,7 +564,12 @@ pub fn generate_pipeline_path(output_path: &std::path::Path) -> String {
 /// Callers are responsible for ensuring the path does not traverse outside the
 /// repository checkout.
 fn normalize_relative_path(path: &std::path::Path) -> Option<String> {
-    if path.is_absolute() {
+    // Detect absolute paths — including Unix-style paths on Windows (which
+    // `Path::is_absolute()` does not recognise because they lack a drive letter).
+    let looks_absolute =
+        path.is_absolute() || path.to_string_lossy().starts_with('/');
+
+    if looks_absolute {
         // Try to make the path relative to the nearest git repo root so that
         // directory structure (e.g. `agents/ctf.md`) is preserved even when
         // the user invokes the compiler with an absolute path.