Fix/accessibility and mock issues

[Jess52487]

closes #100
closes #101
closes #102

Description

This PR resolves three groups of issues related to UI accessibility, connection UX, and test reliability:

1. Badge Accessibility

• Increased the base font size of the Badge component from 9px to 11px to meet WCAG minimum readable size.
• Added a live boolean prop to dynamically updated badges. When true, it applies role="status" and aria-live="polite", ensuring screen readers announce status changes (e.g., transaction outcomes).
• Added aria-hidden="true" to the decorative pulsing dot, preventing it from being announced incorrectly.

2. Wallet Connection UX

• Added clear "Connecting to your wallet…" helper text beneath the connect button while the wallet is connecting.
• Wired up the global error state from SorokitProvider to render an inline error banner on the ConnectScreen.
• Added an interactive dismiss button to the banner that calls clearError().
• Provided a descriptive alt="sorokit wallet dashboard preview" attribute for the hero image to improve screen reader context.

3. Mock Client Reliability

• Replaced the invalid repeating string with a proper Ed25519 Stellar testnet public key.
• Handled unknown network fallbacks explicitly by returning a structured { data: null, error: "Unknown network..." } response, rather than failing silently to testnet.
• Updated MOCK_HISTORY and MOCK_EVENTS to use a deterministic mock generation algorithm rather than module-load-time randHex() calls, ensuring snapshot tests pass consistently across test runs.

Acceptance Criteria met

• All badges render at minimum text-[11px]
• <Badge live> has role="status" and aria-live="polite"
• Dot span has aria-hidden="true"
• Transaction status change is announced by a screen reader
• "Connecting to your wallet…" message visible during connection
• Global error renders on ConnectScreen as an inline banner with dismiss functionality
• Hero image has an alt attribute
• MOCK_ADDRESS passes format check and switchNetwork handles invalid strings properly
• MOCK_HISTORY and MOCK_EVENTS are deterministic
• npm run build and npm run lint pass successfully