feat: add JSON language server support via vscode-json-languageserver (#1404)

* feat: add JSON language server support via vscode-json-languageserver (fixes #1391)

Add support for JSON files using the `vscode-json-languageserver` npm package
from Microsoft. This provides document symbol navigation and hover information
for JSON files.

The implementation follows the existing YAML language server pattern:
- Auto-installs `vscode-json-languageserver` via npm on first use
- Requires Node.js and npm
- Marked as experimental (must be explicitly specified)

Co-Authored-By: Octopus <liyuan851277048@icloud.com>
Co-authored-by: octo-patch <octo-patch@github.com>
Co-authored-by: Michael Panchenko <35432522+MischaPanch@users.noreply.github.com>

test/resources/repos/json/test_repo/config.json

@@ -0,0 +1,24 @@
+{
+  "app": {
+    "name": "test-application",
+    "version": "1.0.0",
+    "port": 8080,
+    "debug": true
+  },
+  "database": {
+    "host": "localhost",
+    "port": 5432,
+    "name": "testdb",
+    "username": "admin"
+  },
+  "logging": {
+    "level": "info",
+    "format": "json",
+    "outputs": ["console", "file"]
+  },
+  "features": {
+    "authentication": true,
+    "caching": false,
+    "monitoring": true
+  }
+}

test/resources/repos/json/test_repo/data.json

@@ -0,0 +1,30 @@
+{
+  "users": [
+    {
+      "id": 1,
+      "name": "Alice",
+      "email": "alice@example.com",
+      "roles": ["admin", "user"]
+    },
+    {
+      "id": 2,
+      "name": "Bob",
+      "email": "bob@example.com",
+      "roles": ["user"]
+    }
+  ],
+  "projects": [
+    {
+      "id": 101,
+      "name": "Project Alpha",
+      "status": "active",
+      "tags": ["backend", "api"]
+    },
+    {
+      "id": 102,
+      "name": "Project Beta",
+      "status": "planning",
+      "tags": ["frontend"]
+    }
+  ]
+}