feat(03-04): replace settings UI with admin-managed placeholder; update API client

- views/SettingsView.vue: Replace full form with static placeholder card. No store
  imports, no API calls. Shows "AI configuration is managed by your administrator."
  (D-12, T-03-21)
- stores/settings.js: Deleted — only consumed by SettingsView; no other imports
- api/client.js: Remove getSettings, patchSettings, testProvider, getDefaultPrompt
  (// Settings section deleted). Add getMyQuota() for quota bar (Plan 03-05).
  Add getUploadUrl() and confirmUpload() for presigned upload flow (Plan 03-05).

frontend/src/api/client.js

@@ -71,6 +71,18 @@ export function classifyDocument(id, topics = null) {
   })
 }
 
+export function getUploadUrl(filename, contentType) {
+  return request('/api/documents/upload-url', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ filename, content_type: contentType }),
+  })
+}
+
+export function confirmUpload(documentId) {
+  return request(`/api/documents/${documentId}/confirm`, { method: 'POST' })
+}
+
 // ── Topics ───────────────────────────────────────────────────────────────────
 
 export function listTopics() {
@@ -105,30 +117,10 @@ export function suggestTopics(documentId) {
   })
 }
 
-// ── Settings ─────────────────────────────────────────────────────────────────
+// ── Quota ────────────────────────────────────────────────────────────────────
 
-export function getSettings() {
-  return request('/api/settings')
-}
-
-export function patchSettings(patch) {
-  return request('/api/settings', {
-    method: 'PATCH',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify(patch),
-  })
-}
-
-export function testProvider(provider) {
-  return request('/api/settings/test-provider', {
-    method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: JSON.stringify({ provider }),
-  })
-}
-
-export function getDefaultPrompt() {
-  return request('/api/settings/default-prompt')
+export function getMyQuota() {
+  return request('/api/auth/me/quota')
 }
 
 // ── Auth ─────────────────────────────────────────────────────────────────────