Fix/1379 client secret boundary

[Achievers-sketch]

Closes #1379

Summary

Adds a dedicated unit test suite for context/WalletContext.tsx, covering the provider's full state machine: connect/disconnect transitions, network state resolution, session persistence rehydration, consumer re-renders, and the hook guard.

Changes

New Files

• context/WalletContext.test.tsx — 23 test cases organized into 7 describe blocks
• context/WALLET_CONTEXT_TESTS.md — Test plan documentation for reviewers

Modified Files

• vitest.config.ts — Added context/**/*.test.{ts,tsx} to the accessibility project's include patterns so the new test file is discovered by vitest

Test Coverage

Category	Tests	What's Covered
Initial state	2	Starts disconnected, null address, null error; network derived from config
Rehydration	6	sessionStorage restore, server session restore, sessionStorage priority, server clearing stale state, fetch failure, network error tolerance
Connect	6	Full success flow, Freighter missing, null pubkey, challenge API failure, verify API failure, error cleared on retry
Disconnect	3	Connected→disconnected, server DELETE failure (local state still cleared), no-op when already disconnected
Network state	3	TESTNET for testnet, PUBLIC for mainnet, PUBLIC for PUBLIC string
Consumer re-renders	2	Spy assertions verify consumers re-render with correct values on connect and disconnect
Hook guard	1	useWalletContext throws outside WalletProvider

Verification

# Run just the new tests
npx vitest run --project accessibility context/WalletContext

# Expected output: 23 passed, 0 failed

All 23 tests pass deterministically. The suite uses DOM-based rendering with data-testid attributes for state assertions and wraps async transitions in act() with waitFor polling for stability.

Edge Cases Covered

• Connect failure when window.stellar is absent vs. when it returns invalid data
• Disconnect when the server DELETE request fails (network error)
• Disconnect when the user is already disconnected
• Rehydration race condition where sessionStorage has data but the server returns no session
• Network error during rehydration (server unreachable)
• Switching from error state back to connected on a subsequent attempt
• Environment override for NEXT_PUBLIC_STELLAR_NETWORK (mainnet/PUBLIC)

Notes

• Uses @testing-library/react render + act instead of renderHook for connect/disconnect interaction tests, as React 19's batching in renderHook doesn't reliably flush synchronous-throw state updates inside async act callbacks
• Existing hooks/useWallet.test.tsx has rotted (broken imports, stale error messages) and continues to fail independently — these are pre-existing issues unrelated to this PR