Update TypeSpec-to-SDK workflow spec with end-to-end design

Rewrites the workflow spec to document the current 6-stage TypeSpec to SDK
release workflow, covering tooling, gaps, and architecture.

Key changes:
- Document all 6 stages with tool tables and identified gaps
- Add architecture section describing current prompt chaining pattern
- Add orchestration improvement gaps (state detection, NextSteps coverage)
- Document auto SDK PR repair (custom code drift fix via Copilot agent)
- Update exceptions with automated namespace approval and arch board review
- Remove outdated release planner references
- Consolidate .NET team integration points

Addresses: #15363

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: samvaity