feat(github): pull request tool window, timeline and review flow (#477)

Replaces the Pull Requests tool window with a full review workflow on top of gh's authentication.

- List with search, quick filters and paging; a tab per pull request and a New Pull Request tab.
- Details: commit picker, changes tree with viewed state, CI and reviewer status, merge, close and reopen.
- Timeline editor: comments, review threads, reactions and suggested changes.
- Review in the diff viewer and, for the checked-out branch, in the editor (review mode).
- New generic vcs extension points: registerDiffViewerProvider, lineInlays, reviewGutter, branch widget extensions; new vcs_merge_base and gh_api commands.
- CSP: img-src allows https://avatars.githubusercontent.com for avatars.

Fixed while testing against a real repository: remotes behind an SSH host alias, mergeability stuck on UNKNOWN, Apply Locally staying disabled after a checkout, relative links navigating the app's page, and review inlays wider than the pane.

Co-authored-by: imacross <[email protected]>

src/editor/api.ts

@@ -276,6 +276,33 @@ export class LaneMarker extends GutterMarker {
   }
 }
 
+/**
+ * The floating row at the editor's top-right (IDEA's inspection widget area): widgets
+ * append their element to it (CSS `order` sorts them; lower first) and remove it when
+ * done. The inspection widget sits there; code review adds its Review Mode group.
+ *
+ *   const el = document.createElement("div");
+ *   el.style.order = "-1";
+ *   editorCorner(view).appendChild(el);
+ */
+export function editorCorner(view: EditorView): HTMLElement {
+  const found = view.dom.querySelector<HTMLElement>(":scope > .cm-openidea-corner");
+  if (found) return found;
+  const el = document.createElement("div");
+  el.className = "cm-openidea-corner";
+  Object.assign(el.style, {
+    position: "absolute",
+    top: "4px",
+    right: "16px",
+    zIndex: "5",
+    display: "flex",
+    alignItems: "center",
+    gap: "4px",
+  });
+  view.dom.appendChild(el);
+  return el;
+}
+
 // --- language support without a language server ----------------------------------
 
 /**

src/editor/lsp/inspectionWidget.ts

@@ -6,6 +6,7 @@
 import { EditorView, ViewPlugin, type ViewUpdate } from "@codemirror/view";
 import { forEachDiagnostic } from "@codemirror/lint";
 import { shortcutLabel } from "@/platform/keymap";
+import { editorCorner } from "@/editor/api";
 import { toolWindowService } from "@/workbench/contributions";
 import { gotoDiagnostic } from "./diagnostics";
 import { iconNode } from "./iconMarkup";
@@ -50,7 +51,7 @@ class InspectionWidget {
     this.dom.className = "cm-openidea-inspection";
     this.dom.setAttribute("role", "toolbar");
     this.dom.setAttribute("aria-label", "Inspections");
-    view.dom.appendChild(this.dom);
+    editorCorner(view).appendChild(this.dom);
     this.render();
   }
 
@@ -123,10 +124,6 @@ const inspectionPlugin = ViewPlugin.fromClass(InspectionWidget);
 
 const inspectionTheme = EditorView.theme({
   ".cm-openidea-inspection": {
-    position: "absolute",
-    top: "4px",
-    right: "16px",
-    zIndex: "5",
     display: "flex",
     alignItems: "center",
     gap: "1px",