Add missing sdk-lite methods for community members and access-check endpoints

[Lakes41]

Difficulty: Intermediate
Type: feature

Background
packages/sdk-lite is described as "a minimal HTTP client for the access API," intended to wrap all four MVP endpoints (/v1/memberships/:wallet, /v1/members/:wallet, /v1/access/check, /v1/communities/:communityId/members).

Problem
As a minimal client, sdk-lite may not yet cover all four endpoints with fully typed methods, forcing consumers to fall back to raw fetch calls for some of them and lose type safety from packages/shared-types.

Expected outcome
sdk-lite exposes a typed method per documented endpoint (getMembershipStatus, getMemberProfile, checkAccess, listCommunityMembers), all using shared request/response types from packages/shared-types, with consistent error handling (throwing a typed SDK error on non-2xx responses).

Suggested implementation

• Audit packages/sdk-lite's current exported methods against the four documented endpoints and fill any gaps.
• Ensure every method's params/return type is imported from packages/shared-types, not locally re-declared.
• Add a small SdkError class capturing status code and parsed error envelope (see error-standardization issue, if implemented alongside).
• Add unit tests using a mocked HTTP layer (e.g., nock or msw) for each method's success and failure paths.

Acceptance criteria

• All four documented endpoints have a corresponding typed SDK method
• Types are sourced from packages/shared-types, not duplicated
• Unit tests cover success and error paths for each method
• README for sdk-lite (or root README) documents usage examples

Likely affected files/directories

• packages/sdk-lite/
• packages/shared-types/