Codebase cleanup: dependency updates, CI hardening, and lint/type fixes

[hazre]

Description

I was really annoyed with all the type errors in the codebase, so I started fixing them but then I kept going and cleanup rest of the codebase as well. I know this is a bit much but I thought I might as well.

• Pinned node and npm version (corepack)
• Updated all dependencies/tooling.
• Updated docker images.
• Migrated ESLint to flat config + typed linting.
• Hardened GitHub workflows, updated actions, pinned with pinact, applied zizmor fixes, and switched setup-node to .node-version.
• Refactored import paths to use aliases for deep imports.
• Resolved all current type and lint errors.
• Updated dependencies with major tooling upgrades and mostly minor runtime updates (with few exceptions).

These are the major changes, everything else is a minor update, so it should be safe.

Major Upgrades

• html-dom-parser (dependencies): 4.0.0 -> ^5.1.8
• i18next (dependencies): 23.12.2 -> 24.10.13
• pdfjs-dist (dependencies): 4.2.67 -> ^5.4.624
• react-i18next (dependencies): 15.0.0 -> ^16.5.4
• @types/node (devDependencies): 18.11.18 -> ^25.2.3
• @vitejs/plugin-react (devDependencies): 4.2.0 -> ^5.1.4
• eslint (devDependencies): 8.29.0 -> ^9.39.2
• eslint-config-prettier (devDependencies): 8.5.0 -> ^10.1.8
• eslint-plugin-react-hooks (devDependencies): 4.6.0 -> ^7.0.1
• prettier (devDependencies): 2.8.1 -> ^3.8.1
• typescript (devDependencies): 4.9.4 -> ^5.9.3
• vite (devDependencies): 5.4.19 -> ^7.3.1
• vite-plugin-pwa (devDependencies): 0.20.5 -> ^1.2.0
• vite-plugin-static-copy (devDependencies): 1.0.4 -> ^3.2.0

Added

• @fontsource-variable/inter (dependency): ^5.2.8
• @eslint/css (devDependency): ^0.14.1
• @eslint/eslintrc (devDependency): ^3.3.3
• @eslint/js (devDependency): ^9.39.2
• typescript-eslint (devDependency): ^8.55.0

Removed

• @fontsource/inter (dependency): 4.5.14
• @typescript-eslint/eslint-plugin (devDependency): 5.46.1
• @typescript-eslint/parser (devDependency): 5.46.1
• eslint-config-airbnb (devDependency): 19.0.4

I've also included a script to normalize the imports, which should help with merge conflicts.

Also worth considering moving to Oxlint and Oxfmt but probably as separate PRs. (I can do it if there is interest)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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
• I have made corresponding changes to the documentation
• My changes generate no new warnings