Feature/adjust colors contrast tool (#4544)

# Description of Changes

- Addition of the "Adjust Colors/Contrast" tool

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/src/components/tools/adjustContrast/utils.ts

@@ -0,0 +1,79 @@
+import { AdjustContrastParameters } from '../../../hooks/tools/adjustContrast/useAdjustContrastParameters';
+
+export function applyAdjustmentsToCanvas(src: HTMLCanvasElement, params: AdjustContrastParameters): HTMLCanvasElement {
+  const out = document.createElement('canvas');
+  out.width = src.width;
+  out.height = src.height;
+  const ctx = out.getContext('2d');
+  if (!ctx) return src;
+  ctx.drawImage(src, 0, 0);
+
+  const imageData = ctx.getImageData(0, 0, out.width, out.height);
+  const data = imageData.data;
+
+  const contrast = params.contrast / 100; // 0..2
+  const brightness = params.brightness / 100; // 0..2
+  const saturation = params.saturation / 100; // 0..2
+  const redMul = params.red / 100; // 0..2
+  const greenMul = params.green / 100; // 0..2
+  const blueMul = params.blue / 100; // 0..2
+
+  const clamp = (v: number) => Math.min(255, Math.max(0, v));
+
+  for (let i = 0; i < data.length; i += 4) {
+    let r = data[i] * redMul;
+    let g = data[i + 1] * greenMul;
+    let b = data[i + 2] * blueMul;
+
+    // Contrast (centered at 128)
+    r = clamp((r - 128) * contrast + 128);
+    g = clamp((g - 128) * contrast + 128);
+    b = clamp((b - 128) * contrast + 128);
+
+    // Brightness
+    r = clamp(r * brightness);
+    g = clamp(g * brightness);
+    b = clamp(b * brightness);
+
+    // Saturation via HSL
+    const rn = r / 255, gn = g / 255, bn = b / 255;
+    const max = Math.max(rn, gn, bn); const min = Math.min(rn, gn, bn);
+    let h = 0, s = 0;
+    const l = (max + min) / 2;
+    if (max !== min) {
+      const d = max - min;
+      s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
+      switch (max) {
+        case rn: h = (gn - bn) / d + (gn < bn ? 6 : 0); break;
+        case gn: h = (bn - rn) / d + 2; break;
+        default: h = (rn - gn) / d + 4; break;
+      }
+      h /= 6;
+    }
+    s = Math.min(1, Math.max(0, s * saturation));
+    const hue2rgb = (p: number, q: number, t: number) => {
+      if (t < 0) t += 1; if (t > 1) t -= 1;
+      if (t < 1/6) return p + (q - p) * 6 * t;
+      if (t < 1/2) return q;
+      if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
+      return p;
+    };
+    let r2: number, g2: number, b2: number;
+    if (s === 0) { r2 = g2 = b2 = l; }
+    else {
+      const q = l < 0.5 ? l * (1 + s) : l + s - l * s;
+      const p = 2 * l - q;
+      r2 = hue2rgb(p, q, h + 1/3);
+      g2 = hue2rgb(p, q, h);
+      b2 = hue2rgb(p, q, h - 1/3);
+    }
+    data[i] = clamp(Math.round(r2 * 255));
+    data[i + 1] = clamp(Math.round(g2 * 255));
+    data[i + 2] = clamp(Math.round(b2 * 255));
+  }
+
+  ctx.putImageData(imageData, 0, 0);
+  return out;
+}
+
+