Add --incdir (-I) flag to script command

Add a global --incdir / -I flag to ScriptArgs that appends user-provided
include directories to both the global all_incdirs and each per-group
TplSrcStruct.incdirs. This ensures custom include paths appear in
per-file-group script output for all formats, not just globally.

Author: DanielKellerM

src/cmd/script.rs

@@ -34,6 +34,10 @@ pub struct ScriptArgs {
     #[arg(short = 'D', long, action = ArgAction::Append, global = true, help_heading = "General Script Options")]
     pub define: Vec<String>,
 
+    /// Add an include directory
+    #[arg(short = 'I', long, action = ArgAction::Append, global = true, help_heading = "General Script Options")]
+    pub incdir: Vec<String>,
+
     /// Remove source annotations from the generated script
     #[arg(long, help_heading = "General Script Options")]
     pub no_source_annotations: bool,
@@ -478,8 +482,13 @@ fn emit_template(
     tera_context.insert("all_defines", &all_defines);
 
     all_incdirs.sort();
+    let user_incdirs: Vec<PathBuf> = args.incdir.iter().map(PathBuf::from).collect();
     let all_incdirs: IndexSet<PathBuf> = if emit_incdirs {
-        all_incdirs.into_iter().map(|p| p.to_path_buf()).collect()
+        all_incdirs
+            .into_iter()
+            .map(|p| p.to_path_buf())
+            .chain(user_incdirs.iter().cloned())
+            .collect()
     } else {
         IndexSet::new()
     };
@@ -530,6 +539,7 @@ fn emit_template(
                             .iter()
                             .map(|p| p.to_path_buf())
                             .collect::<IndexSet<_>>();
+                        incdirs.extend(user_incdirs.iter().cloned());
                         incdirs.sort();
                         incdirs
                     },