test: cover handler pre-auth plugin routing

[richboyneedcash]

/claim #71

Summary

• Add focused Vitest coverage for StarbaseDB.handlePreAuth authless plugin routing.
• Cover dynamic :param and * path prefixes, non-matching paths, auth-required plugins, and authless plugins without a path prefix.
• Keep this scoped to src/handler.test.ts with no production behavior changes.

Verification

• pnpm exec vitest run src/handler.test.ts -> 13 tests passed
• pnpm exec vitest run src/handler.test.ts --coverage.enabled true --coverage.include src/handler.ts --coverage.reporter text --coverage.thresholds.lines=0 --coverage.thresholds.branches=0 --coverage.thresholds.functions=0 --coverage.thresholds.statements=0 -> passed; src/handler.ts reports 65.74% statements / 61.66% branches / 39.28% functions / 67.61% lines in the focused run
• pnpm exec prettier --check src/handler.test.ts -> passed
• git diff --check -> passed

Notes

• No UI demo video is included because this is backend/unit-test-only validation coverage; the verification commands above demonstrate the behavior.
• Current main still has unrelated baseline failures in src/rls/index.test.ts when running the full suite with coverage.
• Transparency: AI-assisted with Codex; I reviewed the diff and verified locally before submitting.