Fold focus-manifest-engine-branch-coverage.test.ts into focus-manifest-engine-barrel.test.ts

[JSONbored]

Part of the '-coverage' bolt-on consolidation epic (#8574 — non-closing reference).

test/unit/focus-manifest-engine-branch-coverage.test.ts (140 lines, describe("focus-manifest engine branch coverage (#2280)")) tests packages/loopover-engine/src/focus-manifest — the same module test/unit/focus-manifest-engine-barrel.test.ts covers.

NOTE the correct merge target: it is the engine-package barrel file, not the 6219-line test/unit/focus-manifest.test.ts, which tests the src-side src/settings/** modules.

Task

• Move the branch cases into focus-manifest-engine-barrel.test.ts with behavior-spec titles; drop any already covered there.
• Delete focus-manifest-engine-branch-coverage.test.ts.
• Verify zero coverage regression on packages/loopover-engine/src/focus-manifest.ts with an unsharded npm run test:coverage before/after comparison.

[linear-code]

JSO-5942