Refactor kantine.js into modular ES6 structure

Moved `kantine.js` into a `src/` directory with multiple modularized files:
- `api.js`: All API calls and constants
- `state.js`: State management (auth, cache, theme, tags, etc.)
- `utils.js`: Helpers for UI and Date formatting
- `ui.js`: DOM manipulation logic
- `events.js`: Initial DOM event listeners and logic hooks
- `actions.js`: Data fetching actions, local processing logic
- `ui_helpers.js`: UI helper functions (rendering modals, handling DOM injections)

Updated the `build-bookmarklet.sh` to compile with Webpack via newly created `webpack.config.js`. Updated all relevant test scripts to use the new output `dist/kantine.bundle.js` and modified logic to work within Webpack scopes.

Co-authored-by: TauNeutrino <1600410+TauNeutrino@users.noreply.github.com>

src/constants.js

@@ -0,0 +1,10 @@
+export const API_BASE = 'https://api.bessa.app/v1';
+export const GUEST_TOKEN = 'c3418725e95a9f90e3645cbc846b4d67c7c66131';
+export const CLIENT_VERSION = 'v1.6.11';
+export const VENUE_ID = 591;
+export const MENU_ID = 7;
+export const POLL_INTERVAL_MS = 5 * 60 * 1000; // 5 minutes
+
+export const GITHUB_REPO = 'TauNeutrino/kantine-overview';
+export const GITHUB_API = `https://api.github.com/repos/${GITHUB_REPO}`;
+export const INSTALLER_BASE = `https://htmlpreview.github.io/?https://github.com/${GITHUB_REPO}/blob`;