Add automatic dedup suffix stripping to enhance syncback functionality

- Introduced a new plan to automatically strip `~N` dedup suffixes from filenames during forward sync, eliminating the need for redundant `.meta.json5` files.
- Implemented the `strip_dedup_suffix()` utility in `dedup_suffix.rs` to handle suffix removal.
- Updated `file_name_for_path()` and `get_dir_middleware()` to utilize the new stripping functionality.
- Modified syncback logic to skip writing meta `name` fields for dedup-only cases, ensuring cleaner instance naming.
- Enhanced existing tests and added new tests to cover the updated dedup behavior, ensuring robustness and correctness.

These changes aim to streamline the handling of deduplicated instances, improving overall system efficiency and clarity in naming conventions.

src/web/api.rs

@@ -1929,7 +1929,7 @@ impl ApiService {
         // not filenames with extensions). This ensures file-format instances
         // are correctly detected as collisions.
         let encoded_name = deduplicate_name(&base_name, sibling_slugs);
-        let needs_meta_name = needs_slug || encoded_name != base_name;
+        let needs_meta_name = needs_slug;
         let meta_name_field: Option<&str> = if needs_meta_name {
             Some(&added.name)
         } else {
@@ -6478,7 +6478,7 @@ mod tests {
                 instance_name.to_string()
             };
             let deduped = deduplicate_name(&base, &taken);
-            let needs_meta = needs_slug || deduped != base;
+            let needs_meta = needs_slug;
 
             fs::create_dir(temp.path().join(&deduped)).unwrap();
 
@@ -6516,7 +6516,7 @@ mod tests {
                     name.to_string()
                 };
                 let deduped = deduplicate_name(&base, &taken);
-                let needs_meta = needs_slug || deduped != base;
+                let needs_meta = needs_slug;
                 taken.insert(deduped.to_lowercase());
                 let meta = if needs_meta {
                     Some(name.to_string())
@@ -6541,7 +6541,7 @@ mod tests {
         fn dir_clean_name_collides_with_existing() {
             let (f, m) = simulate_dir_dedup(&["NewFolder"], "NewFolder");
             assert_eq!(f, "NewFolder~2");
-            assert_eq!(m.unwrap(), "NewFolder");
+            assert!(m.is_none(), "dedup-only: forward sync strips ~N");
         }
 
         #[test]
@@ -6562,14 +6562,14 @@ mod tests {
         fn dir_natural_collides_with_slug() {
             let (f, m) = simulate_dir_dedup(&["A_B"], "A_B");
             assert_eq!(f, "A_B~2");
-            assert_eq!(m.unwrap(), "A_B");
+            assert!(m.is_none(), "dedup-only: forward sync strips ~N");
         }
 
         #[test]
         fn dir_case_insensitive_collision() {
             let (f, m) = simulate_dir_dedup(&["MyFolder"], "myfolder");
             assert_eq!(f, "myfolder~2");
-            assert_eq!(m.unwrap(), "myfolder");
+            assert!(m.is_none(), "dedup-only: forward sync strips ~N");
         }
 
         #[test]
@@ -6628,7 +6628,7 @@ mod tests {
             assert_eq!(r[0].0, "Script");
             assert!(r[0].1.is_none());
             assert_eq!(r[1].0, "Script~2");
-            assert_eq!(r[1].1.as_deref(), Some("Script"));
+            assert!(r[1].1.is_none(), "dedup-only: forward sync strips ~N");
             assert_eq!(r[2].0, "Script~3");
         }
 
@@ -6663,7 +6663,7 @@ mod tests {
             assert_eq!(r[0].0, "CON_");
             assert_eq!(r[0].1.as_deref(), Some("CON"));
             assert_eq!(r[1].0, "CON_~2");
-            assert_eq!(r[1].1.as_deref(), Some("CON_"));
+            assert!(r[1].1.is_none(), "dedup-only: natural CON_ needs no meta");
             assert_eq!(r[2].0, "con_~3");
             assert_eq!(r[2].1.as_deref(), Some("con"));
         }