Address all linting warnings and errors in both backend and frontend code:
**Go (golangci-lint):**
- Add error checking for ignored return values (errcheck)
- Remove unused RPC functions (unused)
- Fix import formatting (goimports)
**TypeScript/React (eslint):**
- Replace all 'any' and 'Function' types with proper type definitions
- Add RpcSendFunction type for consistent JSON-RPC callback signatures
- Fix React Hook exhaustive-deps warnings by adding missing dependencies
- Wrap functions in useCallback where needed to stabilize dependencies
- Remove unused variables and imports
- Remove empty code blocks
- Suppress exhaustive-deps warnings where intentional (with comments)
All linting now passes with 0 errors and 0 warnings.