[L02] Mutation fault injection

[yunseo-kim]

Scope

Add shared fault injection for accepted-then-disconnected, 401/403, 409/422, 5xx, malformed reads, digest delay, stale preflight, and cross-run races.

Contracts

ADRs 0067, 0072-0076

Dependencies

X03

Blocking issues: [X03] #38.

Executable QA

`go test ./internal/npmprofile ./internal/releaseasset ./internal/releasemanifest -run '^(TestMutationFaultMatrix|TestFourStateReduction|TestNoUnsafeRetry)$' -count=1 -v` must exit 0. Every case must have exactly one outcome, expected primary ID, and asserted mutation-call count.