feat: add .env and Claude config downloads to API key reveal

After creating a key, two download buttons appear:
- 'Download .env' — pre-filled FABLE_URL + FABLE_API_KEY
- 'Download Claude config' — ready-to-paste mcpServers JSON block

Also adds Future Task A (in-app install instructions) and Future Task B
(Forgejo MCP) to the implementation plan.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/views/SettingsView.vue

@@ -94,6 +94,38 @@ async function copyApiKey() {
   setTimeout(() => { apiKeyCopied.value = false; }, 2000);
 }
 
+function _downloadFile(filename: string, content: string, mimeType = 'text/plain') {
+  const blob = new Blob([content], { type: mimeType });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = filename;
+  a.click();
+  URL.revokeObjectURL(url);
+}
+
+function downloadEnvFile() {
+  const baseUrl = window.location.origin;
+  const content = `FABLE_URL=${baseUrl}\nFABLE_API_KEY=${newKeyValue.value}\n`;
+  _downloadFile('fable-mcp.env', content);
+}
+
+function downloadMcpConfig() {
+  const baseUrl = window.location.origin;
+  const config = {
+    mcpServers: {
+      fable: {
+        command: 'fable-mcp',
+        env: {
+          FABLE_URL: baseUrl,
+          FABLE_API_KEY: newKeyValue.value,
+        },
+      },
+    },
+  };
+  _downloadFile('fable-mcp-config.json', JSON.stringify(config, null, 2), 'application/json');
+}
+
 // Groups management
 const groups = ref<GroupEntry[]>([]);
 const groupsLoading = ref(false);
@@ -1537,7 +1569,11 @@ function formatUserDate(iso: string): string {
             <code class="api-key-value">{{ newKeyValue }}</code>
             <button @click="copyApiKey" class="btn btn-secondary btn-sm">{{ apiKeyCopied ? 'Copied!' : 'Copy' }}</button>
           </div>
-          <button @click="newKeyValue = ''" class="btn btn-secondary" style="margin-top: 0.5rem;">Done</button>
+          <div style="display:flex; gap:0.5rem; margin-top: 0.5rem;">
+            <button @click="downloadEnvFile" class="btn btn-secondary btn-sm">Download .env</button>
+            <button @click="downloadMcpConfig" class="btn btn-secondary btn-sm">Download Claude config</button>
+            <button @click="newKeyValue = ''" class="btn btn-secondary">Done</button>
+          </div>
         </div>
 
         <!-- Keys table -->