feat: implement mcpctl discover command with table/json/yaml output

Add discover command for searching MCP servers across registries with:
- Table, JSON, YAML output formats
- Filtering by category, verified, transport, registry
- Interactive mode via inquirer
- Dependency injection for testability
- 27 tests covering command parsing, formatting, and action integration

90 tests passing total.

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

.taskmaster/tasks/tasks.json

@@ -750,8 +750,9 @@
         "dependencies": [
           "25"
         ],
-        "status": "pending",
-        "subtasks": []
+        "status": "in-progress",
+        "subtasks": [],
+        "updatedAt": "2026-02-21T03:55:53.004Z"
       },
       {
         "id": "27",
@@ -770,7 +771,7 @@
     ],
     "metadata": {
       "version": "1.0.0",
-      "lastModified": "2026-02-21T03:52:54.909Z",
+      "lastModified": "2026-02-21T03:55:53.004Z",
       "taskCount": 27,
       "completedCount": 2,
       "tags": [