feat(frontend): système de plugins — runtime, menus, layouts custom (#43)

Lots F1-F4 : runtime de chargement/registre plugin, extension des menus
existants, panneau de gestion des plugins, types de layout custom
(sélecteur, fallback, cellule dédiée) branchés sur le port plugin.
Suite npm typecheck/test verte (947/947).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/features/projects/ProjectsView.tsx

@@ -45,6 +45,8 @@ import {
   type SettingsSection,
 } from "@/features/settings";
 import { GitGraphView } from "@/features/git";
+import { usePluginMenus, usePluginRuntime } from "@/features/plugins";
+import type { WhenContext } from "@/plugins/runtime";
 import {
   Button,
   DockRegion,
@@ -112,7 +114,7 @@ function isTerminalBackgroundTaskEvent(
 
 export function ProjectsView() {
   const vm = useProjects();
-  const { system, window: windowGateway, focusedProject } = useGateways();
+  const { system, window: windowGateway, focusedProject, git } = useGateways();
   const [name, setName] = useState("");
   const [root, setRoot] = useState("");
   // Placement of every open view (#22): each panel is "closed" (absent),
@@ -144,6 +146,45 @@ export function ProjectsView() {
 
   const active = vm.openTabs.find((t) => t.id === vm.activeTabId) ?? null;
 
+  // `gitRepository` signal for the plugin `when` mini-language (#43, F3 —
+  // Architect-mandated, blocking for #43 closure): whether the *current*
+  // project is a git repository, checked for real via `GitGateway.branches`
+  // (a non-repo project rejects this call; a repo resolves it). Re-checked on
+  // every project switch. `agentSelected`/`terminalFocused`/
+  // `layoutCellFocused` remain accepted v1 debt — no global focus signal
+  // exists at the menu-bar level yet — and stay `false` (see the F3 report's
+  // open point).
+  const [gitRepository, setGitRepository] = useState(false);
+  useEffect(() => {
+    if (!active) {
+      setGitRepository(false);
+      return;
+    }
+    let cancelled = false;
+    git
+      .branches(active.id)
+      .then(() => {
+        if (!cancelled) setGitRepository(true);
+      })
+      .catch(() => {
+        if (!cancelled) setGitRepository(false);
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [git, active?.id]);
+
+  // Plugin contribution menus (#43, F3).
+  const { registry: pluginRegistry } = usePluginRuntime();
+  const pluginWhenCtx: WhenContext = {
+    projectOpen: active !== null,
+    gitRepository,
+    agentSelected: false,
+    terminalFocused: false,
+    layoutCellFocused: false,
+  };
+  const pluginMenus = usePluginMenus(pluginRegistry, pluginWhenCtx);
+
   // Reset the active layout whenever the active project changes. `activeLayout`
   // is only repopulated asynchronously by `LayoutTabs` (which re-fetches the new
   // project's layouts). Without this reset, the stale id of the *previous*
@@ -391,29 +432,40 @@ export function ProjectsView() {
     {
       id: "panels",
       label: "Panneaux",
-      items: panelOrder.map((panel) => ({
-        id: panel,
-        label: PANEL_TITLE[panel],
-        active: placementOf(placements, panel) !== "closed",
-        onSelect: () => {},
-        submenu: placementSubmenu(panel),
-      })),
+      // Native items first, plugin-contributed items after in their own
+      // (discreetly-labelled) group (#43, F3, carnet §7.2).
+      items: [
+        ...panelOrder.map((panel) => ({
+          id: panel,
+          label: PANEL_TITLE[panel],
+          active: placementOf(placements, panel) !== "closed",
+          onSelect: () => {},
+          submenu: placementSubmenu(panel),
+        })),
+        ...pluginMenus.itemsFor("panels"),
+      ],
     },
+    // Top-level plugin menus render between Panneaux and Paramètres (#43,
+    // carnet §0 UX decision + §7.1).
+    ...pluginMenus.topLevelMenus,
     {
       id: "settings",
       label: "Paramètres",
       // One entry per section (#68). The entries name sections and mark the open
       // one; closing lives in the view ("Fermer les paramètres"), so no label
-      // alternates.
-      items: SETTINGS_SECTIONS.map((section) => ({
-        id: section,
-        label: SETTINGS_SECTION_LABEL[section],
-        active: settingsSection === section,
-        onSelect: () => {
-          setSettingsSection(section);
-          dismissFloating();
-        },
-      })),
+      // alternates. Plugin-contributed items are appended after (#43, F3).
+      items: [
+        ...SETTINGS_SECTIONS.map((section) => ({
+          id: section,
+          label: SETTINGS_SECTION_LABEL[section],
+          active: settingsSection === section,
+          onSelect: () => {
+            setSettingsSection(section);
+            dismissFloating();
+          },
+        })),
+        ...pluginMenus.itemsFor("settings"),
+      ],
     },
   ];
 
@@ -691,6 +743,10 @@ export function ProjectsView() {
                 cwd={active.root}
                 layoutId={activeLayout?.id}
                 onOpenConversation={openConversation}
+                onOpenPluginsSettings={() => {
+                  setSettingsSection("plugins");
+                  dismissFloating();
+                }}
               />
             )}
           </>