Add explicit empty and error states to the slippage view

[BigGoodness]

#closes #658

Pull Request Description

Title

feat(slippage): add empty and error states

---

Description

This PR addresses missing empty and error states for the slippage indicator on the quote view (/quote). It introduces a dedicated SlippageView component with distinct states (empty, loading, error, success), complete with an accessible live region and a retry affordance when requests fail.

---

Requirements & Changes Made

1. Distinct Component & States

• SlippageView: Created a memoized component handling four mutually exclusive states:
  • empty: Indicates no quote or slippage data is present yet ("No slippage data").
  • loading: Indicates quote/slippage calculation is in progress ("Calculating slippage…").
  • error: Indicates an error occurred during quote retrieval, presenting the specific error message and a "Try again" button affordance.
  • success: Displays the computed slippage percentage.

2. Integration

• QuoteClient: Integrated SlippageView into the primary quote workflow, binding lifecycle state to the slippage component and providing a retryQuote callback that re-executes the quote request on retry.

3. Accessibility (WCAG 2.1 AA)

• Wrap state descriptions inside role="status" and aria-live="polite" regions so assistive technology dynamically announces state changes (loading → loaded, error states, and retry actions).
• Keyboard-navigable retry button with focused ring styling consistent with design system conventions.

---

Test Coverage & Test Output

Test File

• Slippage.test.tsx: Comprehensive tests covering empty, loading, success, and error states, as well as checking retry button callback behavior.

Test Execution Output

PASS src/app/quote/Slippage.test.tsx
  SlippageView
    ✓ renders empty state (14 ms)
    ✓ renders loading state (3 ms)
    ✓ renders success state with slippage (4 ms)
    ✓ renders error state with retry button (12 ms)

PASS src/app/quote/QuoteHistory.test.tsx
PASS src/app/quote/page.test.tsx

------------------|---------|----------|---------|---------|-------------------
File              | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------------|---------|----------|---------|---------|-------------------
All files         |   98.24 |    96.42 |   97.82 |   98.11 |                   
  quote/          |   98.15 |    96.15 |   97.50 |   98.05 |                   
    Client.tsx    |   97.80 |    95.83 |   96.87 |   97.75 |                   
    QuoteHistory.tsx|  100.00 |   100.00 |  100.00 |  100.00 |                   
    Slippage.tsx  |  100.00 |   100.00 |  100.00 |  100.00 |                   
------------------|---------|----------|---------|---------|-------------------
Test Suites: 3 passed, 3 total
Tests:       18 passed, 18 total
Snapshots:   0 total
Time:        1.42 s
Ran all test suites matching /src\/app\/quote/.

Coverage Note: Impacted module coverage for src/app/quote exceeds 98%, surpassing the 95% project requirement.

---

Verification Steps

1. Navigate to /quote.
2. Observe initial Empty State ("No slippage data").
3. Submit a valid quote request: view transition to Loading State followed by Success State with calculated slippage.
4. Simulate a network failure or invalid payload: observe Error State with error message and "Try again" button.
5. Click "Try again": verify request re-submits seamlessly.