[codex] fix SPA useSsrCookies default

[cneuralnetwork]

Summary

Fixes #605 by resolving useSsrCookies from Nuxt SSR mode when the option is not explicitly configured.

• Defaults useSsrCookies to false for ssr: false apps so the client plugin uses the non-SSR Supabase client path and restores the session from storage before auth middleware runs.
• Preserves explicit useSsrCookies: true or false settings.
• Documents SPA / CSR-only behavior and the changed default.
• Adds focused unit coverage for the resolver.

Validation

• vitest run test/resolveUseSsrCookies.test.ts
• targeted ESLint on changed code files
• vue-tsc --noEmit -p tsconfig.json
• npm run build
• git diff --check

Note: full npm run lint was blocked locally because the npm-based setup did not generate demo/.nuxt/eslint.config.mjs; the targeted changed-file lint passed.

[vercel]

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[pkg-pr-new]

npm i https://pkg.pr.new/@nuxtjs/supabase@607

commit: 490a371