feat: add Content-Security-Policy header and externalize theme-init #177

Job	Run time
Performance benchmarks (informational)	26s
Frontend unit tests (vitest) (macos-latest)	29s
mypy	19s
Frontend unit tests (vitest) (windows-latest)	44s
pytest (ubuntu-latest)	42s
Verify prod requirements.txt is sufficient	8s
Frontend unit tests (vitest) (ubuntu-latest)	18s
API integration tests + coverage (macos-latest)	21s
pytest (macos-latest)	26s
API integration tests + coverage (windows-latest)	1m 8s
ruff + pip-audit (macos-latest)	24s
ruff + pip-audit (windows-latest)	59s
ruff + pip-audit (ubuntu-latest)	19s
pytest (windows-latest)	1m 30s
API integration tests + coverage (ubuntu-latest)	19s
	8m 32s

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