docs: add v11.x forward roadmap section to NEXT_STEPS.md

[satwareAG-ironMike]

Problem

After listing all v11.0 items as complete, NEXT_STEPS.md ends with a stale work log and no forward-looking section. There is no v11.1.0 or v12.0.0 roadmap.

Fix

Add a "## Roadmap" section with:

• v11.0.x maintenance items (linking to the v11.0.1 milestone)
• v11.1.0 quality hardening items (linking to the v11.1.0 milestone)
• v12.0.0 OOP completion goals (linking to the v12.0.0 milestone)

Source

QA Audit 2026-04-09 - Finding D10 (Priority P3)