Refactor/separate db logic from react components

[JuanTorres93]

Description

Fixes #10

Extracts all raw Dexie.js database queries out of React components and into dedicated service files under src/services/db/, following the separation of concerns described in the issue.

New service files

Each file groups database operations for a single domain:

• dbContents.js
• dbContests.js
• dbFormulas.js
• dbGate.js
• dbHabits.js
• dbJobs.js
• dbPomodoros.js
• dbProblems.js
• dbQuickLinks.js
• dbSettings.js
• dbSnippets.js
• dbTasks.js

Refactored components

All database logic removed from: Dashboard, ContentCurator, FormulaVault, JobTracker, HabitTracker, LeetCode, Pomodoro, Profile, SnippetBoard, TodoList, GatePrep, and popup.jsx.

Custom hook

Introduced useDBQuery — a reusable hook that handles calling DB service functions, reducing boilerplate across components and keeping the UI synchronized with database updates.

Type of change

• Maintenance / Refactoring (non-functional changes)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce.

• Verified locally via Extension loading in developer mode.
• Checked for console errors or warnings.
• Verified UI looks good and behaves correctly.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings