Senator Roster Page UI

[msonal1]

Motivation:
Students need visibility into who represents them; the senator roster is a core transparency feature. This PR implements the roster page with search, sort, and navigation, and establishes the pattern for future data tables in the app.

Changes:

• Added /senators/roster/page.tsx with a Shadcn Table displaying headshot, full name, district, committee assignments, and email
• Added client-side search input that filters senators by name
• Made name and district columns sortable via header clicks
• Clicking a senator's row or name navigates to /senators/[id]
• Wired the table to getSenators() from the API client, with mock data fallback
• Added headshot fallback that renders initials when headshot_url is null
• Formatted committee assignments as "Finance (Member), Rules (Vice Chair)" from the nested CommitteeAssignmentDTO list
• Made the table horizontally scrollable on mobile

Closes #14

[github-actions]

Test Results

555 tests  ±0   555 ✅ ±0   5s ⏱️ ±0s
  1 suites ±0     0 💤 ±0 
  1 files   ±0     0 ❌ ±0 

Results for commit f4cbb6a. ± Comparison against base commit 2f010ba.

♻️ This comment has been updated with latest results.

[calebyhan]

LGTM, had to do some funny force push smth, hope this works