feat: add response-ledger route with action history and ownership rail

[iamasx]

Summary

• Adds a new /response-ledger route with mock action history, outcome summaries, and a compact ownership rail
• Includes 8 mock action entries with status badges (completed, in-progress, escalated, deferred), 8 outcome summary cards, and per-owner resolution tracking
• Adds nav link in layout and showcase section on the home page
• Includes test coverage for page rendering, action list, outcomes, and ownership rail

Closes #212

Test plan

• Verify /response-ledger renders action history entries with status badges
• Verify outcome summary cards display with correct result indicators
• Verify ownership rail shows owner counts and resolution rates
• Verify responsive layout across common breakpoints
• Run vitest run src/app/response-ledger/page.test.tsx to confirm tests pass

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