feat: add editor component

docs/CHECKLIST.md

@@ -9,18 +9,15 @@ is the first downstream consumer; its screens drive the order.
 
 ## Next
 
-- [ ] **Scrollbar** (M13) — a simple way to show a scrollbar on gpui's
-      `list` and `uniform_list`.
-    - [x] API sketch
-    - [x] Implementation (theme-baked, overlays virtualized lists)
-    - [x] Tests
-    - [x] Gallery panel
+- [ ] **Diff view** (M15, `editor`).
+    - [ ] API sketch
+    - [ ] Implementation
+    - [ ] Tests
+    - [ ] Gallery panel
     - [ ] Review
 
 ## Queue — to follow
 
-- [ ] **Code view** (M14, opens `crates/editor`) — tree-sitter highlighting.
-- [ ] **Diff view** (M15, `editor`).
 - [ ] **Markdown view** (M16, `editor`) — only if a consumer confirms.
 - [ ] **Pickers** — Calendar / DatePicker, TimeField, ColorPicker (decide at
       unit time).
@@ -61,12 +58,20 @@ is the first downstream consumer; its screens drive the order.
       screen-reader label
 - [x] Combobox — type-to-filter picker, create / keep / revert blur modes
 - [x] Command palette — filtered actions; the matcher stays caller-owned
+- [x] Scrollbar — overlay thumbs for gpui's `list` and `uniform_list`,
+      platform autohide with a `visibility` override
 
 ### data (`crates/data`)
 
 - [x] List, Tree, Tabs (underline default + signed pill), Sidebar (scrolls
       internally)
 
+### editor (`crates/editor`)
+
+- [x] Code view — tree-sitter highlighted, virtualized rows with a gutter
+      and the overlay scrollbar; per-language grammar features, roles map to
+      the theme's semantic palette at render
+
 ### layout (`crates/layout`)
 
 - [x] ResizeHandle