Refactor extension internals and add repo-wide quality checks

[MaximilianMauroner]

Summary

Refactor the extension into focused content/shared modules, centralize settings and cache contracts, and add lint/test coverage with fixture-backed DOM parsing tests.
Align product metadata and popup wording with actual behavior, and update CI to run the broader repository validation flow.

Why

• Reduce maintenance risk from the monolithic content script and duplicated settings logic
• Add automated checks for brittle parsing and row-detection behavior before future changes
• Keep repo, manifest, popup, and release docs consistent with the extension's actual scope

Testing

• bun run check
• Verified typecheck, ESLint, Vitest, build, Firefox lint, release validation, and packaging locally

Future improvements

• Add browser-level integration coverage against real GitHub markup snapshots to catch DOM regressions earlier
• Tighten latest-activity extraction to use a more explicit signal if GitHub exposes one reliably
• Consider pruning repeated build work in CI/release scripts to reduce validation time

Confidence

Component	Score	Notes
Content script refactor	4	Behavior preserved through module extraction and local validation
Shared settings/cache contracts	5	Logic is centralized and covered by unit tests
Test and lint tooling	4	New checks pass locally and are wired into CI
Docs and release metadata	5	Scope and wording now match the implemented extension

[Copilot]

Pull request overview

This PR refactors the extension’s content-script internals into focused content/ and shared/ modules, centralizes settings/cache contracts, and adds repo-wide quality checks (ESLint + Vitest with fixture-backed DOM parsing tests) that are now run in CI/release workflows.

Changes:

• Split the monolithic content script into modular content/shared files (DOM parsing, rendering, fetching, storage, cache, settings).
• Add Vitest (jsdom) tests with HTML fixtures covering settings/cache behavior and GitHub DOM parsing/extraction helpers.
• Add ESLint flat config and expand CI/release workflows to run bun run check (typecheck + lint + test + release validations).

Reviewed changes

Copilot reviewed 33 out of 34 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
vitest.config.ts	Adds Vitest jsdom configuration for DOM-focused unit tests.
tsconfig.tests.json	Introduces a dedicated TS config for test typechecking.
tests/.test.ts + tests/helpers/fixtures.ts + tests/fixtures/.html	Adds fixture-backed parsing/extraction tests for settings, cache payloads, and GitHub DOM variations.
src/shared/types.ts	Exports shared extension contracts (settings, cache payloads, row model, etc.).
src/shared/settings.ts	Centralizes default settings + sanitization/merge behavior.
src/shared/cache.ts	Centralizes cache versioning and persisted payload helpers.
src/popup.ts	Switches popup logic to use shared settings/cache contracts.
src/content/*	New modular content-script implementation (DOM selection/parsing, extractors, fetch queue, render, storage wrapper, app bootstrap).
src/content.ts	Replaces the monolithic script with a thin bootstrap wrapper.
eslint.config.mjs	Adds ESLint flat config for src/scripts/tests with TS support.
package.json	Adds lint/test scripts and a repo-wide check script; expands typecheck to include tests.
scripts/check-release.ts	Tightens typing for built manifest validation.
popup.html / README.md / manifest.json / docs/release-checklist.md	Aligns wording/scope with current PR-list-only behavior and updates release/check instructions.
.github/workflows/ci.yml / release.yml	Updates CI/release to run bun run check.
bun.lock	Locks newly added lint/test dependencies.

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