fix(cli): recognize --no-upload option, decouple --json from upload

Summary

• Fix --no-upload option not being recognized in checkup command
• Remove automatic --no-upload implication when --json is used (now independent)
• Add comment documenting the decoupled behavior
• Add comprehensive tests for upload flag combinations

Tests added

• --upload and --no-upload options are recognized
• --json does not imply --no-upload (decoupled behavior)
• --json --upload requires API key
• --json --no-upload disables upload
• --upload requires API key (without config)
• --no-upload does not require API key

Test plan

• bun test checkup.test.ts passes (70 tests)
• bun ./bin/postgres-ai.ts checkup --help shows both options
• bun ./bin/postgres-ai.ts checkup postgresql://... --no-upload no longer errors with "unknown option"

Closes #100 (closed)

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