Consolidate plugin management UI

[xiami762]

Summary

• Add a unified Plugin Management entry with tabs for agents, skills, tools, and the plugin marketplace.
• Keep Device Integration as a separate primary navigation entry while redirecting legacy agent/skill/tool/hub routes into Plugin Management.
• Add plugin enable/disable support in the hub API and surface enabled state in catalog entries.
• Refine embedded Agent, Skill, Tool, and Hub views for a denser management experience.

Validation

• npm run lint
• npm run build
• git diff --check
• uv run ruff check flocks/hub flocks/server/routes/hub.py tests/hub/test_hub_catalog.py
• uv run pytest tests/hub/test_hub_catalog.py tests/hub/test_bundled_tools.py