Add admin console and improve import compatibility

[sarihuangshanrong]

Summary

This PR adds a web admin console for context-hub and introduces import history visibility in the Import
page.

Admin console

• add pages for dashboard, content browsing, search, document viewing, import, and settings
• add shared layout, navigation, tree view, and markdown preview components
• add the server-side handlers needed to support the console
• remove EASE branding from the console shell

Import improvements

• add single-file and batch zip import support in the console
• improve batch import compatibility for mixed markdown archives
• normalize Windows-style zip paths before classification and planning
• improve skill/doc handling for SKILL.md-style archives

Import history

• persist import history for single-file and batch imports
• add import history list/detail API endpoints
• add a History tab to the Import page
• show recent import runs and per-run details in the UI

Testing

• node cli/src/index.js build content --validate-only
• cd server/web && npm run build
• manually verified /api/v1/import/history
• manually verified the Import page History tab