feat(p8): vue IDE /workspace (arbre + Monaco + diff + terminal)

- backend: garde-fou conflit d'édition par mtime (GET renvoie mtime, PUT refuse en 409 STALE_FILE si baseMtime périmé)
- lib: wt-key (base64url du chemin worktree), diff-parse (parseur pur du diff unifié → hunks)
- composables: useMonaco (import dynamique → chunk isolé), useWorkspaceLayout (largeurs/panneau persistés)
- components/workspace: GitStatusBadge, FileTree+FileTreeNode (lazy fs/list includeFiles), ChangedFilesPanel, DiffViewer (coloration +/-), MonacoEditor (Ctrl+S + bannière conflit reload/overwrite)
- views/WorkspaceView: 3 colonnes desktop redimensionnables + SegmentedControl mobile, header live (GitStatusBadge), watchWorktree → refresh diff/changements, terminal de la session corrélée
- router meta 'ide' + route /workspace/:repoId/:wt ; App.vue plein écran sans AppShell ; WorktreeCard bouton « Ouvrir l'IDE »
- deps: monaco-editor (lazy, vendor-monaco isolé, 0 impact bundle initial) ; vite manualChunks
- i18n EN+FR (workspace/editor/diff/git) ; tests diff-parse + wt-key ; acceptance-p8.mjs (mtime/409 + diff)

packages/web/src/components/workspace/FileTree.vue

@@ -0,0 +1,57 @@
+<template>
+  <div class="flex h-full flex-col">
+    <div class="flex items-center gap-1 px-2 py-1 text-[11px] font-semibold uppercase tracking-wide text-zinc-500">
+      <FolderTree :size="13" /> {{ t('workspace.files') }}
+      <button type="button" class="ml-auto rounded p-0.5 hover:bg-zinc-800 hover:text-zinc-300" :title="t('common.refresh')" @click="load">
+        <RefreshCw :size="12" />
+      </button>
+    </div>
+    <div class="min-h-0 flex-1 overflow-auto px-1 pb-2">
+      <p v-if="loading" class="px-2 py-1 text-xs text-zinc-600">{{ t('fs.loading') }}</p>
+      <p v-else-if="error" class="px-2 py-1 text-xs text-rose-400">{{ error }}</p>
+      <p v-else-if="entries.length === 0" class="px-2 py-1 text-xs text-zinc-600">{{ t('fs.empty') }}</p>
+      <FileTreeNode
+        v-for="e in entries"
+        :key="e.path"
+        :entry="e"
+        :wt="wt"
+        :depth="0"
+        :active="active"
+        @open="(p) => emit('open', p)"
+      />
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { onMounted, ref, watch } from 'vue';
+import { useI18n } from 'vue-i18n';
+import { FolderTree, RefreshCw } from '@lucide/vue';
+import type { FsEntry, FsListResponse } from '@arboretum/shared';
+import { api } from '../../lib/api';
+import FileTreeNode from './FileTreeNode.vue';
+
+const props = defineProps<{ wt: string; active: string | null }>();
+const emit = defineEmits<{ open: [relPath: string] }>();
+const { t } = useI18n();
+
+const entries = ref<FsEntry[]>([]);
+const loading = ref(false);
+const error = ref<string | null>(null);
+
+async function load(): Promise<void> {
+  loading.value = true;
+  error.value = null;
+  try {
+    const res = await api.get<FsListResponse>(`/api/v1/fs/list?path=${encodeURIComponent(props.wt)}&includeFiles=1`);
+    entries.value = [...res.entries].sort((a, b) => Number(!!a.isFile) - Number(!!b.isFile) || a.name.localeCompare(b.name));
+  } catch (err) {
+    error.value = err instanceof Error ? err.message : String(err);
+  } finally {
+    loading.value = false;
+  }
+}
+
+onMounted(load);
+watch(() => props.wt, load);
+</script>