chore: vendor ML/CV libraries for panel detection

Add machine learning and computer vision libraries to vendor/ directory
to support panel detection feature. Following foliate-js's existing pattern
of vendoring large dependencies (similar to pdf.js at 13MB).

Vendored libraries (~12.5MB):
- vendor/tfjs/tf.min.js (1.5MB): TensorFlow.js UMD build
  * Downloaded from unpkg.com during build via custom Rollup plugin
  * Required runtime for COCO-SSD model

- vendor/opencv/opencv.js (~11MB): OpenCV.js UMD build
  * Copied from @techstark/opencv-js npm package
  * Provides edge detection and image processing
  * Requires 'unsafe-eval' CSP directive due to eval() usage

- vendor/coco-ssd/coco-ssd.min.js (~9KB): COCO-SSD model
  * Copied from @tensorflow-models/coco-ssd npm package
  * Pre-trained object detection for irregular panel layouts

Total vendor size: ~25MB (was 13MB, added 12.5MB)

These UMD/global builds ensure browser compatibility without requiring
ES module imports, which would cause bare specifier errors in browsers.
All libraries are loaded dynamically via script injection when panel
detection is first used, minimizing initial load time.

vendor/tfjs/tf.min.js

@@ -1,6 +1,6 @@
 /**
  * @license
- * Copyright 2018 Google LLC. All Rights Reserved.
+ * Copyright 2024 Google LLC. All Rights Reserved.
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -14,35 +14,5 @@
  * limitations under the License.
  * =============================================================================
  */
-import '@tensorflow/tfjs-core';
-// tslint:disable-next-line: no-imports-from-dist
-import '@tensorflow/tfjs-core/dist/register_all_gradients';
-// tslint:disable-next-line: no-imports-from-dist
-import '@tensorflow/tfjs-core/dist/public/chained_ops/register_all_chained_ops';
-export * from '@tensorflow/tfjs-core';
-export * from '@tensorflow/tfjs-layers';
-export * from '@tensorflow/tfjs-converter';
-// Export data api as tf.data
-import * as data from '@tensorflow/tfjs-data';
-export { data };
-// Import and register backends.
-export * from '@tensorflow/tfjs-backend-cpu';
-export * from '@tensorflow/tfjs-backend-webgl';
-// Import versions of all sub-packages.
-import { version_core } from '@tensorflow/tfjs-core';
-import { version_cpu } from '@tensorflow/tfjs-backend-cpu';
-import { version_webgl } from '@tensorflow/tfjs-backend-webgl';
-import { version_data } from '@tensorflow/tfjs-data';
-import { version_layers } from '@tensorflow/tfjs-layers';
-import { version_converter } from '@tensorflow/tfjs-converter';
-import { version as version_union } from './version';
-export const version = {
-    'tfjs-core': version_core,
-    'tfjs-backend-cpu': version_cpu,
-    'tfjs-backend-webgl': version_webgl,
-    'tfjs-data': version_data,
-    'tfjs-layers': version_layers,
-    'tfjs-converter': version_converter,
-    'tfjs': version_union
-};
-//# sourceMappingURL=index.js.map
+!function(e,t){"object"==typeof exports&&"undefined"!=typeof module?t(exports):"function"==typeof define&&define.amd?define(["exports"],t):t((e="undefined"!=typeof globalThis?globalThis:e||self).tf=e.tf||{})}(this,(function(e){"use strict";function t(e,t){return t.forEach((function(t){t&&"string"!=typeof t&&!Array.isArray(t)&&Object.keys(t).forEach((function(n){if("default"!==n&&!(n in e)){var r=Object.getOwnPropertyDescriptor(t,n);Object.defineProperty(e,n,r.get?r:{enumerable:!0,get:function(){return t[n]}})}}))})),e}var n="undefined"!=typeof globalThis?globalThis:"undefined"!=typeof window?window:"undefined"!=typeof global?global:"undefined"!=typeof self?self:{};function r(e){return e&&e.__esModule&&Object.prototype.hasOwnProperty.call(e,"default")?e.default:e}function a(e){var t,n;function r(t,n){try{var o=e[t](n),s=o.value,u=s instanceof i;Promise.resolve(u?s.v:s).then((function(n){if(u){var i="return"===t?"return":"next";if(!s.k||n.done)return 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+//# sourceMappingURL=tf.min.js.map