refactor(platform): rename SmartDecisionMakerBlock to OrchestratorBlock (#12511)

## Summary
- Renames `SmartDecisionMakerBlock` to `OrchestratorBlock` across the
entire codebase
- The block supports iteration/agent mode and general tool
orchestration, so "Smart Decision Maker" no longer accurately describes
its capabilities
- Block UUID (`3b191d9f-356f-482d-8238-ba04b6d18381`) remains unchanged
— fully backward compatible with existing graphs

## Changes
- Renamed block class, constants, file names, test files, docs, and
frontend enum
- Updated copilot agent generator (helpers, validator, fixer) references
- Updated agent generation guide documentation
- No functional changes — pure rename refactor

### For code changes
- [x] I have clearly listed my changes in the PR description
- [x] I have made corresponding changes to the documentation
- [x] My changes do not generate new warnings or errors
- [x] New and existing unit tests pass locally with my changes

## Test plan
- [x] All pre-commit hooks pass (typecheck, lint, format)
- [x] Existing graphs with this block continue to load and execute (same
UUID)
- [x] Agent mode / iteration mode works as before
- [x] Copilot agent generator correctly references the renamed block