feat(desktop): refine repository-aware project workspaces (#6003)

## Summary
- Makes Projects repository-aware across browsing, branch and tag
selection, local and remote source management, work items, commits, and
contextual repository actions.
- Refines project details into consistent single-column reading surfaces
with a resizable, section-aware context pod, while keeping project
conversations available in the attached chat panel.
- Adds persistent sidebar project navigation, direct entity links,
repository discussion channels, contributor identity matching, and
consistent loading and activity presentation.
- Keeps branch-specific controls on code-oriented sections while Tasks,
Reviews, and Channels remain repository-scoped, reducing misleading
context and actions.

Replacement for #5981 with an identical final tree flattened into one
signed-off commit because the required DCO check suite remained stalled.

### Related issue
N/A

### Testing
- [x] Desktop pre-push checks, TypeScript typecheck, and unit tests
- [x] E2E production build with `pnpm build:e2e`
- [x] Focused Playwright smoke coverage for project workspace, task,
review, commit, sidebar, and contextual-panel behavior
- [ ] Attach final before/after screenshots after design review

---------

Signed-off-by: Thomas Petersen <thomasp@squareup.com>
Signed-off-by: Wintermute <165f0c871dd2586bb18b6aa109eeaf57bb2132ff4d27b10120f4368a0f627022@buzz.block.builderlab.xyz>
Co-authored-by: Wintermute <165f0c871dd2586bb18b6aa109eeaf57bb2132ff4d27b10120f4368a0f627022@buzz.block.builderlab.xyz>

desktop/src/features/projects/useProjectRepositoryRefSelection.ts

@@ -5,14 +5,34 @@ export function useProjectRepositoryRefSelection(input: {
   defaultBranch: string | null;
   projectAvailable: boolean;
   projectPending: boolean;
+  /** Identity of the repository the options describe. A switch to a
+   * different repository resets the selection even when the new repository
+   * happens to have a branch or tag with the same name — carrying `release`
+   * from repo A into repo B would silently retarget files, actions, and
+   * agent context at a ref the user never chose. */
+  repositoryId: string | null;
   tags: Array<{ name: string }>;
 }) {
   const [selectedBranch, setSelectedBranch] = React.useState<string | null>(
     null,
   );
   const [selectedTag, setSelectedTag] = React.useState<string | null>(null);
+  const [selectionRepositoryId, setSelectionRepositoryId] = React.useState(
+    input.repositoryId,
+  );
+  // Reset during render (not in an effect) so a repository switch can never
+  // paint one frame with the previous repository's same-named selection.
+  if (selectionRepositoryId !== input.repositoryId) {
+    setSelectionRepositoryId(input.repositoryId);
+    setSelectedBranch(null);
+    setSelectedTag(null);
+  }
+  const staleSelection = selectionRepositoryId !== input.repositoryId;
   const activeBranch =
-    selectedBranch ?? input.defaultBranch ?? input.branchOptions[0] ?? null;
+    (staleSelection ? null : selectedBranch) ??
+    input.defaultBranch ??
+    input.branchOptions[0] ??
+    null;
 
   React.useEffect(() => {
     if (!input.projectAvailable) {
@@ -52,7 +72,7 @@ export function useProjectRepositoryRefSelection(input: {
   return {
     activeBranch,
     selectBranch,
-    selectedTag,
+    selectedTag: staleSelection ? null : selectedTag,
     selectTag,
   };
 }