Document all possible errors with causes and solutions.
Acceptance Criteria:
- Create error catalog markdown document
- List all ContractError variants with: description, common cause, solution
- List all SDK-thrown errors (network, simulation, timeout)
- Add troubleshooting section
- Link from README
Files: new file docs/errors.md, README.md
Document all possible errors with causes and solutions.
Acceptance Criteria:
Files: new file
docs/errors.md,README.md