Rename GSD→SF: complete rebrand from fork origin
- All gsdDir/gsdRoot/gsdHome → sfDir/sfRootDir/sfHome
- GSDWorkspace* → SFWorkspace* interfaces
- bootstrapGsdProject → bootstrapProject
- runGSDDoctor → runSFDoctor
- GsdClient → SfClient, gsd-client.ts → sf-client.ts
- .gsd/ → .sf/ in all tests, docs, docker, native, vscode
- Auto-migration: headless detects .gsd/ → renames to .sf/
- Deleted gsd-phase-state.ts backward-compat re-export
- Renamed bin/gsd-from-source → bin/sf-from-source
- Updated mintlify docs, github workflows, docker configs
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