Add new endpoint to allow users to update the encrypted vault payload
after initial setup. This enables adding, editing, and removing venue
credentials without requiring a full vault re-initialization.

Changes:
- Add PUT /vault/payload to OpenAPI spec
- Implement UpdateVaultPayload handler with server-side validation
- Require both encrypted and decrypted payloads for validation
- Validate vault must be unsealed and session must be active
- Validate decrypted payload structure and venue configuration
- Use existing UpsertVaultPayload storage method (atomic transaction)
- Sync venue metadata to storage after successful update

The endpoint validates:
- Session authentication and vault unsealed state
- Encrypted payload structure (version, ciphertext, nonce)
- Decrypted payload contents using vault.Data.Validate()
- At least one primary venue exists
- No duplicate venue IDs
- Valid wallet addresses (40 hex chars)
- Valid private keys (64 hex chars)

After update, the vault remains unsealed but new configuration
is not active until seal/re-unseal cycle.

Co-authored-by: Claude <[email protected]>

The generated UpdateVaultPayload200JSONResponse has Message as *string,
but the handler was passing a string literal. Fixed to use a pointer.

Also add comprehensive test coverage for UpdateVaultPayload endpoint
covering all scenarios from the spec:
- Success case with valid payload
- Missing/invalid session (401)
- Vault sealed (403)
- No primary venue (400)
- Multiple primary venues (400)
- Duplicate venue IDs (400)
- Invalid wallet address (400)
- Invalid private key (400)
- Database errors (500)

Co-authored-by: Claude <[email protected]>

Fix test failures:
- Use VenueId field instead of ID in VenueRecord
- Pass vault.StateSealed to NewController (signature changed)

Co-authored-by: Claude <[email protected]>

Fix all UpdateVaultPayload tests to properly inject HTTP request
into context. The requireSession() function needs the HTTP request
in the context to work properly, even in debug mode.

Changes:
- Add net/http and net/http/httptest imports
- Create httptest.NewRequest for each test
- Add request to context using httpRequestContextKey
- Pass context with request to handler

Co-authored-by: Claude <[email protected]>

Co-authored-by: Your Name <[email protected]>

…hanging-functionality

test: fix vault payload update tests