Reject unsafe typeof suppression in defensive.null-assumption rule

[alxxjohn]

Motivation

• The previous change treated any whole-function occurrence of typeof <param> ===/== as a null guard, which allows unsafe patterns like typeof x === "object" (note typeof null === "object") or non-dominating checks to suppress defensive.null-assumption findings.

Description

• Remove the broad "typeof <name> ===" / "typeof <name> ==" entries from the nullable-parameter guard list in nullableParamGuarded so arbitrary whole-function typeof occurrences no longer count as guards.
• Tighten nullableStatementUsesOnlyNullSafeOperators to preserve only safe, same-statement TypeScript narrowing patterns by matching a typeof-based ternary narrowing that directly dereferences the narrowed value in the same expression.
• Add a regression test TestDefensiveNullAssumptionRejectsUnsafeTypeofGuards in tests/checks/quality_precision_followup_retune_test.go that asserts unsafe typeof usages (e.g. typeof user === 'object' and a late typeof after an unsafe dereference) still trigger defensive.null-assumption.
• Modified files: internal/codeguard/checks/quality/quality_defensive.go and tests/checks/quality_precision_followup_retune_test.go.

Testing

• Ran the focused test group with go test ./tests/checks -run 'TestDefensiveNullAssumption(CreditsTypeScriptNarrowing|RejectsUnsafeTypeofGuards)$' -count=1, which passed.
• Ran full test suite with go test ./... after fixing test assertions, which completed successfully for the repository packages that include tests.
• Applied gofmt -w to the modified files and validated git diff --check produced no whitespace issues during the edit cycle.

---

Codex Task