Fix stdio CLI help and parse errors

[wowsofine]

Summary

• add --help / -h handling for the Supabase MCP stdio CLI before server startup
• normalize unknown top-level flag parse errors to a concise stderr message and exit 1
• add integration coverage for help output and unknown flag behavior

Closes #296.

Validation

• Red test first: CI=1 npx --yes pnpm@10.33.2 --filter @supabase/mcp-server-supabase exec vitest run --project integration test/stdio.integration.ts failed on the new help/unknown-flag assertions before the fix
• npx --yes pnpm@10.33.2 --filter @supabase/mcp-utils build
• npx --yes pnpm@10.33.2 --filter @supabase/mcp-server-supabase build
• CI=1 npx --yes pnpm@10.33.2 --filter @supabase/mcp-server-supabase test:unit
• CI=1 npx --yes pnpm@10.33.2 --filter @supabase/mcp-server-supabase exec vitest run --project integration test/stdio.integration.ts
• npx --yes pnpm@10.33.2 format:check
• dist smoke: --help and -h exit 0 and print usage
• dist smoke: --version exits 0 and prints 0.8.2
• dist smoke: unknown flag exits 1 and does not print ERR_PARSE_ARGS_UNKNOWN_OPTION
• git diff --check

I also ran the full package test command. Unit and integration coverage passed, while the e2e tests failed because ANTHROPIC_API_KEY is not available in my local environment.