Hoist collectUnmappedSrc helper in selectE2eSpecs so unmapped risk-area
files are computed before the high-risk early-return. When high-risk wins
and risk files lack a manifest entry, the curated result now includes
them in unmapped and appends '; curated + risk files without mapping: ...'
to reason — mode stays curated.
Pin: testAffected gains combined case (migration + unmapped risk file →
curated with unmapped in reason). Closes#846.
