Dark Contracts 1.0.3: Corrected mutation harness

Test and tooling release. No contract or circuit changes: the deployed bytecode is unchanged and still reproduces from this release byte-for-byte.

Changes

• The mutation harness (contracts/script/mutate.mjs) now runs an unmutated baseline first, copies everything the suite needs into its scratch tree, and counts a mutant as killed only when a test assertion fails; a mutant that fails to compile is reported separately as invalid. The previous harness could report a mutant as killed because of a setup error.
• Re-run on the corrected harness: 44 mutants, 44 killed, 0 survived, 0 invalid. Four new mutants exposed a gap, now covered by new tests in contracts/test/DarkVault.t.sol.
• Depends on Dark SDK 0.4.3.