Update deduplication logic and documentation for suffix handling

- Removed the `luau` dependency from `rokit.toml`.
- Updated deduplication logic to append `~2`, `~3`, etc. instead of `~1`, `~2` for naming collisions in various files, ensuring consistent suffix management.
- Adjusted comments and documentation across multiple files to reflect the new suffix handling rules.
- Added new test cases to validate the updated deduplication behavior, ensuring accurate naming for instances with collisions.

These changes enhance the clarity and functionality of the deduplication process, improving overall consistency in naming conventions.

.cursor/rules/atlas-syncback.mdc

@@ -145,8 +145,8 @@ Manages `~N` suffix cleanup after instance deletions during two-way sync.
 - `compute_cleanup_action(removed_stem, remaining_stems) -> DedupCleanupAction` - Determine what to do after a deletion
 
 **Cleanup rules:**
-- **Gap-tolerant:** Deleting `~1` from `{Foo, Foo~1, Foo~2}` leaves `{Foo, Foo~2}`. No renumbering.
-- **Base-name promotion:** Deleting `Foo` (base) from `{Foo, Foo~1, Foo~2}` promotes `Foo~1` to `Foo`. `Foo~2` stays.
+- **Gap-tolerant:** Deleting `~2` from `{Foo, Foo~2, Foo~3}` leaves `{Foo, Foo~3}`. No renumbering.
+- **Base-name promotion:** Deleting `Foo` (base) from `{Foo, Foo~2, Foo~3}` promotes `Foo~2` to `Foo`. `Foo~3` stays.
 - **Group-to-1 cleanup:** If group shrinks to 1 member, remove its suffix entirely.
 
 ## Syncback Rules
@@ -285,12 +285,12 @@ snapshot.with_new_path(path, new_ref, old_ref)
 
 **Filename generation** (`file_names.rs`):
 - `slugify_name()`: forbidden chars (`<>:"/\|?*~`) → `_`. Also strips leading/trailing spaces/dots, neutralizes dangerous suffixes (`.server`, `.meta`, etc.), handles Windows reserved names (`CON`, `PRN`, etc.)
-- `deduplicate_name_with_ext()`: Dedup key = full filesystem name (slug + extension), case-insensitive. `Folder "Foo"` (key `"foo"`) and `Script "Foo"` (key `"foo.server.luau"`) do NOT collide. Appends `~1`, `~2`, etc. on collision, with suffix inserted before compound extension: `Foo~1.server.luau`
+- `deduplicate_name_with_ext()`: Dedup key = full filesystem name (slug + extension), case-insensitive. `Folder "Foo"` (key `"foo"`) and `Script "Foo"` (key `"foo.server.luau"`) do NOT collide. Appends `~2`, `~3`, etc. on collision, with suffix inserted before compound extension: `Foo~2.server.luau`
 - `name_for_inst()` returns `(filename, needs_meta_name, dedup_key)`. `needs_meta_name` is true when the filesystem name differs from the real instance name.
 - `~` is in `SLUGIFY_CHARS` so natural tilde names (e.g., `"Foo~1"`) get slugified to `"Foo_1"`, avoiding confusion with dedup suffixes.
 - Example: `Script` named "My Script" → `My Script.server.luau`
 - Example: `Script` named "Hey/Bro" → `Hey_Bro.server.luau` + meta with `name: "Hey/Bro"`
-- Example: Two `Folder "Data"` → `Data/` + `Data~1/` (meta: `name: "Data"`)
+- Example: Two `Folder "Data"` → `Data/` + `Data~2/` (meta: `name: "Data"`)
 
 ### Property Filtering