Add --single-line output option to emit flattened SQL for batching

[simbo1905]

Feature request: Add a CLI option (e.g., --single-line) to make the generated Jinja2 output emit as a single SQL line, suitable for batching in simple line-based runners.

Context:

• Manual approvals/agents often require per-line inputs; multi-line SQL creates friction.
• We currently post-process with awk/sed to flatten.

Scope:

• Parser/CLI: accept --single-line (default false).
• Render: if enabled, collapse whitespace/newlines while preserving SQL semantics.
• Docs: note the flag and example use; mention batching patterns.
• Tests: add a basic check for one-line output shape (e.g., no newlines) while preserving key tokens (CREATE/SELECT/JOIN).