feat: hide entry content from list, add GET /api/entries/:id/content endpoint

Content is no longer returned in the entries list. A separate endpoint
returns plain text content for clipboard copying on demand.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "files": [],
+  "references": [
+    { "path": "./tsconfig.app.json" },
+    { "path": "./tsconfig.node.json" }
+  ]
+}