feat(phase-4): frontend data layer — API client (13 new functions), folders store, documents store extensions, routes

- Extended listDocuments to accept folderId, q, sort, order query params
- Added 6 folder API functions: listFolders, createFolder, getFolder, renameFolder, deleteFolder, moveDocument
- Added 4 share API functions: createShare, listShares, deleteShare, getSharedWithMe
- Added 2 preference API functions: getMyPreferences, updateMyPreferences
- Added getDocumentContentUrl helper (returns URL string, no fetch)
- Created useFoldersStore with full CRUD, navigation state, and breadcrumb support
- Extended useDocumentsStore with currentFolderId, searchQuery, sortField, sortOrder refs
- Added debounced searchQuery watcher (300ms, 2-char minimum, T-04-08-03)
- Added shareDocument, revokeShare, listShares actions to documents store
- Added /folders/:folderId and /shared routes with requiresAuth guard

frontend/src/stores/documents.js

@@ -1,5 +1,5 @@
 import { defineStore } from 'pinia'
-import { ref } from 'vue'
+import { ref, watch } from 'vue'
 import * as api from '../api/client.js'
 import { useAuthStore } from './auth.js'
 
@@ -34,12 +34,16 @@ export const useDocumentsStore = defineStore('documents', () => {
   const error = ref(null)
   // uploadProgress: keyed by "${file.name}__${Date.now()}" to prevent collision (T-03-25)
   const uploadProgress = ref({})
+  const currentFolderId = ref(null)
+  const searchQuery = ref('')
+  const sortField = ref('date')
+  const sortOrder = ref('desc')
 
-  async function fetchDocuments({ topic, page = 1, perPage = 20 } = {}) {
+  async function fetchDocuments({ topic, page = 1, perPage = 20, folderId = null, q = null, sort = null, order = null } = {}) {
     loading.value = true
     error.value = null
     try {
-      const data = await api.listDocuments({ topic, page, perPage })
+      const data = await api.listDocuments({ topic, page, perPage, folderId, q, sort, order })
       documents.value = data.items
       total.value = data.total
     } catch (e) {
@@ -125,5 +129,30 @@ export const useDocumentsStore = defineStore('documents', () => {
     return result.topics
   }
 
-  return { documents, total, loading, error, uploadProgress, fetchDocuments, upload, remove, reclassify }
+  // Debounced search watcher: fires after 300 ms; ignores inputs shorter than 2 chars (T-04-08-03)
+  let _searchTimer = null
+  watch(searchQuery, (newVal) => {
+    clearTimeout(_searchTimer)
+    if (newVal.length < 2) {
+      fetchDocuments({ folderId: currentFolderId.value })
+      return
+    }
+    _searchTimer = setTimeout(() => {
+      fetchDocuments({ q: newVal, folderId: currentFolderId.value, sort: sortField.value, order: sortOrder.value })
+    }, 300)
+  })
+
+  async function shareDocument(docId, recipientHandle) {
+    try { return await api.createShare(docId, recipientHandle) } catch (e) { throw e }
+  }
+
+  async function revokeShare(shareId) {
+    try { await api.deleteShare(shareId) } catch (e) { throw e }
+  }
+
+  async function listShares(docId) {
+    try { return await api.listShares(docId) } catch (e) { throw e }
+  }
+
+  return { documents, total, loading, error, uploadProgress, currentFolderId, searchQuery, sortField, sortOrder, fetchDocuments, upload, remove, reclassify, shareDocument, revokeShare, listShares }
 })

frontend/src/stores/folders.js

@@ -0,0 +1,85 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+import * as api from '../api/client.js'
+
+export const useFoldersStore = defineStore('folders', () => {
+  const folders = ref([])
+  const currentFolderId = ref(null)
+  const breadcrumb = ref([])
+  const loading = ref(false)
+  const error = ref(null)
+
+  async function fetchFolders(parentId = null) {
+    loading.value = true
+    error.value = null
+    try {
+      const data = await api.listFolders(parentId)
+      folders.value = data
+    } catch (e) {
+      error.value = e.message || 'Failed to load folders'
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function createFolder(name, parentId = null) {
+    loading.value = true
+    error.value = null
+    try {
+      const folder = await api.createFolder(name, parentId)
+      folders.value.push(folder)
+      return folder
+    } catch (e) {
+      error.value = e.message || 'Failed to create folder'
+      throw e
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function renameFolder(folderId, name) {
+    loading.value = true
+    error.value = null
+    try {
+      const updated = await api.renameFolder(folderId, name)
+      const idx = folders.value.findIndex(f => f.id === folderId)
+      if (idx !== -1) folders.value[idx] = updated
+      return updated
+    } catch (e) {
+      error.value = e.message || 'Failed to rename folder'
+      throw e
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function deleteFolder(folderId) {
+    loading.value = true
+    error.value = null
+    try {
+      await api.deleteFolder(folderId)
+      folders.value = folders.value.filter(f => f.id !== folderId)
+    } catch (e) {
+      error.value = e.message || 'Failed to delete folder'
+      throw e
+    } finally {
+      loading.value = false
+    }
+  }
+
+  async function navigateTo(folderId) {
+    currentFolderId.value = folderId
+    if (folderId != null) {
+      try {
+        const data = await api.getFolder(folderId)
+        breadcrumb.value = data.breadcrumb || []
+      } catch (e) {
+        breadcrumb.value = []
+      }
+    } else {
+      breadcrumb.value = []
+    }
+  }
+
+  return { folders, currentFolderId, breadcrumb, loading, error, fetchFolders, createFolder, renameFolder, deleteFolder, navigateTo }
+})