feat(web): coquille IDE + arbre de projets unifié (route /ide)

components/ide/ : IdeShell (grille barre d'activité + panneau gauche + zone centrale + dock + barre de statut, splitters persistés, réconciliation des ressources ouvertes contre les données live), ActivityBar (Explorer/Git/Sessions/Groupes + Réglages/Aide), PrimarySidebar, ProjectTree + ProjectTreeNode (arbre unique repos -> worktrees -> sessions, fichiers embarqués via FileTree en mode sans chrome, dépliage paresseux), StatusBar.

Route /ide (layout 'ide'), entrée de nav « IDE », namespace i18n ide (EN/FR). Clics de l'arbre pilotent le store (contexte worktree, ouverture de fichier/terminal). Centre et dock en placeholders (remplis en B4/B5). FileTree gagne un mode embedded. 427 tests.

packages/web/src/i18n/en.ts

@@ -218,6 +218,27 @@ export default {
     noSession: 'No session here',
     noSessionHint: 'Start a session on this worktree from the dashboard to get a terminal.',
   },
+  ide: {
+    projects: 'Projects',
+    addProject: 'Add project',
+    noProjects: 'No project yet. Add one to get started.',
+    noWorktrees: 'No worktree',
+    activity: {
+      explorer: 'Explorer',
+      git: 'Git',
+      sessions: 'Sessions',
+      groups: 'Groups',
+    },
+    startClaude: 'Start Claude',
+    startBash: 'Start bash',
+    noFileOpen: 'No file open',
+    noFileHint: 'Pick a file in the tree to edit it, or a changed file to view its diff.',
+    terminals: 'Terminals',
+    noTerminal: 'No terminal open',
+    noTerminalHint: 'Open a Claude session from the tree to attach a terminal here.',
+    comingSoon: 'Coming soon',
+    ready: 'Ready',
+  },
   editor: {
     save: 'Save',
     unsaved: 'Unsaved changes',
@@ -332,6 +353,7 @@ export default {
     reconnecting: 'Connection lost. Reconnecting…',
   },
   nav: {
+    ide: 'IDE',
     worktrees: 'Worktrees',
     sessions: 'Sessions',
     groups: 'Groups',