chore(010): scaffold ESLint, Prettier, Vitest, node:test, CI, VS Code config

[astrobyte-dev]

Closes the tooling-scaffolding portion of issue 010.

Stands up the static-check + test + build layer so every later issue's "done" criteria (npm run lint, npm test, npm run build) actually resolve. No production code touched except a single dead duplicate width key in VideoPlayer.jsx (user-approved one-line exception).

Highlights

• Root: .editorconfig, .prettierrc.json, .prettierignore, .gitattributes, engines.node >= 22, lint/test scripts fanning out via npm workspaces.
• Frontend: ESLint flat config (warn-baseline for legacy code), Vitest + jsdom + Testing Library, @/ alias in vite.config.js and jsconfig.json, 4 real tests of formatDuration.
• Backend: ESLint flat config, node --test auto-discovery (Node 22+), supertest available for future route tests, 6 real tests of sanitizeLimit / sanitizeSort.
• VS Code: recommended-extensions list + workspace settings (formatOnSave, fixAll.eslint on save, per-package eslint.workingDirectories).
• CI: .github/workflows/ci.yml runs install / lint / test / build on Node 22 for every push and PR.
• memory.md updated; new decisions log entry records warn-baseline, Node 22 floor, react-hooks v7 strategy, and the no-dupe-keys one-line exception.

Local verification

• npm run lint (root): 0 errors, 43 warnings, exit 0
• npm test (root): 10 tests passed (6 backend, 4 frontend), exit 0
• npm run build (root): exit 0
• Deliberate parse error: lint exits 1, returns to 0 when reverted.

Scope kept tight

The modified README.md, feed-mode-prd.md, CLAUDE.md, TESTING.md, and issues/011-019.md are intentionally NOT in this PR; they're a separate concern from tooling and will land in their own changes.

Follow-ups (not in this PR)

• Two no-constant-binary-expression warnings in LightboxModal.jsx look like real logic bugs; recommend addressing during that file's shrink, not under 010.
• 4 npm audit findings (3 moderate, 1 high) appeared post-install; deferred (would need npm audit fix --force, which is explicitly forbidden per CLAUDE.md).

🤖 Generated with Claude Code

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[Copilot]

Pull request overview

This PR scaffolds the monorepo’s developer tooling so linting, testing, and builds are consistently runnable locally and in CI (issue 010), while keeping production code changes minimal.

Changes:

• Adds workspace-level scripts and a Node 22+ engine floor to standardize lint/test/build execution.
• Sets up ESLint (flat config) + Prettier for both frontend and backend, plus Vitest (jsdom) for frontend and node --test for backend with initial unit tests.
• Adds VS Code workspace configuration and a GitHub Actions CI workflow to run install/lint/test/build on pushes and PRs.

Reviewed changes

Copilot reviewed 21 out of 22 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
package.json	Renames package, adds Node engine floor, adds workspace lint/test scripts.
memory.md	Documents project “memory”, current state, and tooling decisions for issue 010.
frontend/vitest.config.js	Configures Vitest to run in jsdom with setup file and @/ alias.
frontend/vite.config.js	Adds @/ path alias resolution to Vite config.
frontend/src/utils/format.test.js	Adds unit tests for formatDuration.
frontend/src/test/setup.js	Adds test setup importing Testing Library matchers.
frontend/src/components/VideoPlayer.jsx	Removes a dead duplicate width key in inline style object.
frontend/package.json	Adds lint/test scripts and devDependencies for ESLint/Prettier/Vitest/Testing Library.
frontend/jsconfig.json	Adds JS path mapping for @/* and module resolution settings for editor tooling.
frontend/eslint.config.js	Adds frontend ESLint flat config including react + react-hooks and Prettier integration.
backend/src/utils/normalizePost.test.js	Adds backend unit tests for sanitizeLimit and sanitizeSort using node:test.
backend/package.json	Adds lint/test scripts and devDependencies for ESLint + supertest.
backend/jsconfig.json	Adds backend JS project config for editor tooling.
backend/eslint.config.js	Adds backend ESLint flat config and Prettier integration.
.vscode/settings.json	Adds workspace formatting and ESLint-on-save settings with per-package working directories.
.vscode/extensions.json	Recommends ESLint/Prettier and assistant extensions for contributors.
.prettierrc.json	Adds Prettier formatting configuration.
.prettierignore	Ignores node_modules, dist, and package-lock from formatting.
.github/workflows/ci.yml	Adds CI workflow running install/lint/test/build on Node 22.
.gitattributes	Normalizes line endings to LF for text files.
.editorconfig	Adds editor defaults (2-space indent, LF, trim whitespace, etc.).

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