Improve GitHub panel toolbar and loading states (#1664)

* feat(app): add toolbar and loading states to the GitHub PR panel

Adds a toolbar under the PR title with a refresh button (refreshes git
and GitHub status + timeline in one tap), an always-visible View Pull
Request button, and a Merge control with a method dropdown that is
disabled-with-reason when the PR can't be merged yet.

The merge control reuses the existing git-actions policy verbatim via a
new buildPrPanelMergeActions selector fed into GitActionsSplitButton, so
no merge readiness/squash/auto-merge logic is duplicated.

Also replaces the empty-state flash with skeletons: a full-panel
skeleton while PR status loads and an activity skeleton while the
timeline loads, with empty states shown only when loaded-and-empty and
an error state with retry.

* refactor(app): tidy PR panel skeleton (i18n, shared pulse, index)

Addresses review feedback on the PR panel work:
- Localize the skeleton's "Checks" label via t() instead of hardcoding.
- Hoist the shared SkeletonPulse + useSkeletonPulse into activity-skeleton
  so pane-skeleton reuses them instead of duplicating the pulse driver.
- Export PullRequestPaneError/Skeleton from the module index and import
  them through it, matching the module's existing public surface.

* test(app): remove mock-based PR pane test

* fix(app): simplify PR panel toolbar

* fix(app): report PR panel retry failures

packages/app/src/i18n/resources.test.ts

@@ -243,6 +243,7 @@ describe("translation resources", () => {
     expect(en.workspace.git.actions.commit.label).toBe("Commit");
     expect(en.workspace.git.diff.binaryFile).toBe("Binary file");
     expect(en.workspace.git.pr.sections.checks).toBe("Checks");
+    expect(en.workspace.git.pr.actions.viewPullRequest).toBe("View");
     expect(en.review.comment.placeholder).toBe("Leave a comment");
   });
 

packages/app/src/i18n/resources/ar.ts

@@ -717,6 +717,9 @@ export const ar: TranslationResources = {
         failedOpen: "فشل في فتح مساحة العمل",
       },
       pr: {
+        actions: {
+          viewPullRequest: "عرض",
+        },
         sections: {
           checks: "الشيكات",
           reviews: "التعليقات",

packages/app/src/i18n/resources/en.ts

@@ -724,6 +724,9 @@ export const en = {
         failedOpen: "Failed to open workspace",
       },
       pr: {
+        actions: {
+          viewPullRequest: "View",
+        },
         sections: {
           checks: "Checks",
           reviews: "Reviews",

packages/app/src/i18n/resources/es.ts

@@ -744,6 +744,9 @@ export const es: TranslationResources = {
         failedOpen: "No se pudo abrir el espacio de trabajo",
       },
       pr: {
+        actions: {
+          viewPullRequest: "Ver",
+        },
         sections: {
           checks: "cheques",
           reviews: "Reseñas",

packages/app/src/i18n/resources/fr.ts

@@ -743,6 +743,9 @@ export const fr: TranslationResources = {
         failedOpen: "Échec de l'ouverture de l'espace de travail",
       },
       pr: {
+        actions: {
+          viewPullRequest: "Voir",
+        },
         sections: {
           checks: "Chèques",
           reviews: "Avis",

packages/app/src/i18n/resources/ru.ts

@@ -736,6 +736,9 @@ export const ru: TranslationResources = {
         failedOpen: "Не удалось открыть рабочую область",
       },
       pr: {
+        actions: {
+          viewPullRequest: "Открыть",
+        },
         sections: {
           checks: "Чеки",
           reviews: "Отзывы",

packages/app/src/i18n/resources/zh-CN.ts

@@ -711,6 +711,9 @@ export const zhCN: TranslationResources = {
         failedOpen: "打开 workspace 失败",
       },
       pr: {
+        actions: {
+          viewPullRequest: "查看",
+        },
         sections: {
           checks: "Checks",
           reviews: "Reviews",