Add state search combobox and active state chips

[PavelMakarchuk]

Summary

• Add a search combobox in the sticky header for finding states by name or abbreviation, with bill count indicators
• Replace the static "States with Major Tax Changes" placeholder with dynamic teal pill chips showing states that have published analysis
• Expose statesWithBills count object from DataContext for both components

Test plan

• Page loads with search input in header and chips in placeholder panel
• Typing filters states by name or abbreviation; Enter navigates to state
• Arrow keys navigate dropdown, Escape/click-outside closes it
• Chips show all states with published (non-in_review) bills as teal pills with count badges
• Clicking a chip navigates to that state
• URL routing and iframe postMessage still work

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