Fix dependency security and test toolchain compatibility

[suciudan]

Resolve the five pending dependency updates and remove the remaining esbuild security alert. The React plugin update failed because version 6 requires Vite 8 while the dashboard used Vite 7.

• Upgrade Vite to 8.3.0 with Vitest 5.0.0, React plugin 6.1.1, and Testing Library React 16.3.3. Group future updates to this toolchain in Dependabot.
• Update Knex to 3.3.0 across its three workspaces and Nodemailer to the patched 10.0.x line (lockfile: 10.0.10).
• Scope an esbuild 0.25.12 resolution to the legacy Drizzle loader, removing GHSA-67mh-4wv8-2f99. The current Payload/Drizzle dependency tree still includes that loader. Add CI regression checks for TypeScript transforms, relative configuration imports, and the real OTP template through a stubbed SES transport.
• Run the full dependency audit in CI without severity exclusions and document the override's compatibility risk and removal conditions.

Validation on Node 24.21.0 / Yarn 4.9.2: immutable install; full audit with no advisories; API/SDK unit suites; 112 dashboard integration tests on disposable SQLite; dashboard types and lint (one pre-existing warning); both production builds; five new dependency compatibility tests; and a disposable MySQL check covering schema creation, insert, lookup, and transaction rollback passed. No UI or application logic changes. No email, production requests, deployments, or package publishing.

Replaces #11, #12, #13, #14, and #15 after this validated replacement merges. Addresses Dependabot alert #1 by changing the dependency tree, without dismissing the alert.

Prepared with AI assistance. All five required hosted CI checks passed, including the full dependency audit, compatibility regressions, integration suites, and both application builds.