Session list performance: disk summary cache, display-name cache, and count alignment #246

Job	Run time
Performance benchmarks (gated)	33s
Verify prod requirements.txt is sufficient	9s
Frontend unit tests (vitest) (ubuntu-latest)	22s
API integration tests + coverage (ubuntu-latest)	17s
Frontend unit tests (vitest) (macos-latest)	30s
API integration tests + coverage (macos-latest)	17s
mypy	24s
Frontend unit tests (vitest) (windows-latest)	1m 32s
pytest (ubuntu-latest)	45s
ruff + pip-audit (macos-latest)	21s
pytest (macos-latest)	34s
ruff + pip-audit (windows-latest)	54s
pytest (windows-latest)	1m 19s
ruff + pip-audit (ubuntu-latest)	20s
API integration tests + coverage (windows-latest)	55s
	9m 12s

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