feat: v0.2.1 - Library separation and NuGet packaging - #5

…roundwork

…eDbc/validateConfig/generateCode + async + path orchestration)

… DbcParserLib dependency; fix regex quoting

…) and wire Api.generateCode; add Codegen.fs to project

…; smoke E2E PASS\nfeat(Facade): add C#-friendly thin facade wrapping Core (exceptions instead of Result)\ndocs: GEMINI Progress updated (2025-08-27)

…ifacts; pack preview0 for Core/Facade

…preview.0, refine NuGet READMEs; build/tests green

…n and docs; confirm pack; prep for v0.2.1 tag

…to avoid NuGet reservation conflict

…elease workflow

- Add NuGet version badges for SignalCandy and SignalCandy.Core packages
- Modify release workflow to only deploy from main branch (prevents accidental releases from feature branches)
- Release workflow now checks if tag is reachable from main before proceeding with NuGet publish