2.x gap: port remaining burn hotspots CLI modes

[willwashburn]

From the Rust 2.x gap catalog.

Current 2.x status:

• burn hotspots supports the default attribution view, --json, --all, and --group-by for single-axis rollups.
• The Rust SDK already supports pattern findings, but the CLI presenter is not fully wired.

Missing from 1.x parity:

• Per-session mode: --session [id]
• --explain-drift
• --patterns
• --findings
• --workflow
• --provider

Acceptance:

• Wire the remaining CLI modes over the SDK surface.
• Preserve clear refusal/error behavior for genuinely unsupported combinations.
• Add tests/golden coverage for session, findings, and filtered modes.
• Update docs/help to match the implemented surface.