chore(config): upgrade eslint, ci, and vscode tasks to match backend template

[cH0NKIIs34L]

Summary

Upgrades ESLint rules, CI pipeline, and VS Code task runner to match
the conventions established in the backend template, then cleans up
all lint and format errors the stricter config surfaced.

What Changed

• eslint.config.js — stricter no-unused-vars (args, caught errors);
  react-refresh and react-hooks overrides for providers and effects
• .github/workflows/ci.yml — single serial job → four parallel jobs
  (test, lint, format-check, build); Supabase placeholder env vars added
  to the build step
• .vscode/tasks.json — added Format: Check task and CI: Verify All
  compound task that mirrors all four CI jobs locally

Screenshots / Demo

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What

This PR brings the template repo's tooling config into parity with
the backend template across ESLint, GitHub Actions CI, and VS Code tasks.

Why

The frontend template had drifted from the backend template's conventions,
making it harder to apply the same workflow habits across both repos —
particularly around catching more categories of unused variables and
being able to verify CI locally before pushing.

How

• ESLint's no-unused-vars was extended with argsIgnorePattern,
  caughtErrors: 'all', and caughtErrorsIgnorePattern to match
  the backend template's stricter stance without requiring changes
  to existing code patterns
• CI was split into four parallel jobs instead of one serial job
  so failures are isolated and pipelines run faster
• The build job sets VITE_SUPABASE_* placeholder env vars so
  Vite doesn't fail when import.meta.env references are present
  but no .env file exists in CI
• @supabase/supabase-js was added to package.json dependencies
  in anticipation of Supabase integration
• After the config upgrade, npm run lint:fix and npm run format
  were run to clean up all errors surfaced by the stricter rules

Testing

• Ran npm run test:run — all tests pass
• Ran npm run lint — no errors
• Ran npm run format:check — no errors
• Ran npm run build — succeeds with placeholder Supabase env vars set
• Opened VS Code task runner and confirmed ✅ CI: Verify All runs
  all four jobs in parallel

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Pre-Merge Checklist

• Synced with main before opening this PR (git fetch origin && git merge origin/main)
• All tests pass locally (npm test)
• No console.log left in production code
• Self-reviewed my own diff before requesting review
• Added or updated tests for the changes made
• No new ESLint errors (npm run lint)