docs: define BYOL synthesis license model

[hkimw]

Summary

• add a BYOL synthesis license model covering local, isolated VM, and hybrid flows
• define the LicenseProvider / BitstreamRequest / BuildResult boundary without adding runtime execution
• document customer-owned Vivado / Quartus activation, no vendor license secret ingress, and legal-review gates

Validation

• PATH="$PWD/.venv/bin:$PATH" make strict
• PATH="$PWD/.venv/bin:$PATH" make lint
• git diff --check

Closes #104

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