Adopt the Fleet code-health quality gate

[sarthakagrawal927]

Adopt the Fleet-wide measurable code-health contract in Calorie: whole-source coverage floors, unused code and dependency checks, complexity and exact-duplication ratchets, import-cycle detection, severe-advisory allowlisting, suppression-marker ceilings, repository hygiene, and one CI-enforced quality command. Remove behavior-neutral dead code and safe dependency debt found during adoption. Follow-up debt that cannot be removed safely will be tracked separately.

[sarthakagrawal927]

Adoption is implemented in draft PR #31 at 25b642c.

Final evidence:

• Web/Worker: 148 tests across 36 files; 22.34% line, 17.07% branch, 22.78% function, and 21.69% statement coverage across the complete production denominator.
• Native: 16 unit tests and 3 UI tests; Release build; 3,057/5,616 production Swift lines covered (54.4338%) against a portable 54.30% floor.
• Zero Knip findings, zero TypeScript import cycles, and zero critical/high dependency advisories.
• Complexity and duplication are measured and regression-gated; one reviewed suppression remains.
• GitHub CI is green for both check and native-quality on the final commit.
• Cleanup audit receipt: run_b2386a1a349f253ab4c7aa95c7729a5b.