feat: add link_type field to quick links

Adds link_type column to quick_links table for iframe vs new_tab behavior.
Includes Alembic migration and schema updates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "core-api"
-version = "1.6.0"
+version = "1.6.1"
 description = "Core Code API - Infrastructure management and tools API"
 readme = "README.md"
 requires-python = ">=3.12"