feat: add Content-Security-Policy header and externalize theme-init #168

Job	Run time
Frontend unit tests (vitest) (ubuntu-latest)	15s
Frontend unit tests (vitest) (macos-latest)	19s
ruff + pip-audit (ubuntu-latest)	23s
ruff + pip-audit (windows-latest)	1m 15s
ruff + pip-audit (macos-latest)	25s
pytest (windows-latest)	1m 1s
API integration tests + coverage (ubuntu-latest)	18s
mypy	19s
pytest (ubuntu-latest)	43s
pytest (macos-latest)	24s
API integration tests + coverage (macos-latest)	27s
API integration tests + coverage (windows-latest)	59s
Frontend unit tests (vitest) (windows-latest)	47s
Verify prod requirements.txt is sufficient	10s
Performance benchmarks (informational)	27s
	8m 12s

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