feat: search functionality and shared ui components

[HelderMendes]

Standardizes search across all entity types and adds shared UI components.

Search — per entity

• Search pages, containers and result cards for: Datasets, Flows, Tasks, Runs, Collections, Benchmarks, Users
• Per-entity search configs (search-config.ts) defining filters, sort options and facets

Search — shared

• FilterBar — unified filter controls used across all search pages
• SearchTabs — tab navigation between entity search views
• UrlSearchSync — syncs search state (query, filters, sort) to the URL for shareability
• StudySearchPage — shared base for collection/benchmark search pages

Header & layout

• SearchBar — updated global search bar in the header
• Sidebar — refactored sidebar navigation