refactor(frontend): decouple signature status logic from PDF color palette (#6992)

# Description of Changes

- Moved the signature status-to-color mapping from `signatureStatus.ts`
to `pdfPalette.ts`.
- Removed the PDF palette dependency from the pure signature status
calculation module.
- Updated the PDF signature report to import the color mapping from the
palette module.
- Prevented signature status unit tests from initializing
browser-dependent CSS colors unnecessarily.
- Eliminated fallback warnings caused by unavailable theme CSS variables
in the Vitest environment.
- Preserved the existing signature status calculation and PDF report
color behavior.

```sh
[frontend:test:editor] stderr | src/core/hooks/tools/validateSignature/utils/signatureStatus.test.ts
[frontend:test:editor] CSS variable --pdf-light-header-bg not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-accent not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-text-primary not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-text-muted not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-box-bg not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-box-border not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-warning not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-danger not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-success not found, using fallback
[frontend:test:editor] CSS variable --pdf-light-neutral not found, using fallback
```

---

## 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/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)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### 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 run `task check` to verify linters, typechecks, and tests
pass
- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#7-testing)
for more details.

frontend/editor/src/core/hooks/tools/validateSignature/outputtedPDFSections/SignatureSection.ts

@@ -3,12 +3,12 @@ import { PdfiumFont, PdfiumPage } from "@app/services/pdfiumDocBuilder";
 import { SignatureValidationSignature } from "@app/types/validateSignature";
 import { drawFieldBox } from "@app/hooks/tools/validateSignature/outputtedPDFSections/FieldBoxSection";
 import { drawStatusBadge } from "@app/hooks/tools/validateSignature/outputtedPDFSections/StatusBadgeSection";
-import {
-  computeSignatureStatus,
-  statusKindToPdfColor,
-} from "@app/hooks/tools/validateSignature/utils/signatureStatus";
+import { computeSignatureStatus } from "@app/hooks/tools/validateSignature/utils/signatureStatus";
 import { formatDate } from "@app/hooks/tools/validateSignature/utils/pdfText";
-import { colorPalette } from "@app/hooks/tools/validateSignature/utils/pdfPalette";
+import {
+  colorPalette,
+  statusKindToPdfColor,
+} from "@app/hooks/tools/validateSignature/utils/pdfPalette";
 
 interface DrawSignatureSectionOptions {
   page: PdfiumPage;

frontend/editor/src/core/hooks/tools/validateSignature/utils/pdfPalette.ts

@@ -1,4 +1,5 @@
 import { rgb } from "@app/services/pdfiumDocBuilder";
+import type { SignatureStatusKind } from "@app/hooks/tools/validateSignature/utils/signatureStatus";
 
 type RgbTuple = [number, number, number];
 
@@ -93,3 +94,16 @@ export const colorPalette = {
     defaultLightPalette.neutral,
   ),
 };
+
+export const statusKindToPdfColor = (kind: SignatureStatusKind) => {
+  switch (kind) {
+    case "valid":
+      return colorPalette.success;
+    case "warning":
+      return colorPalette.warning;
+    case "invalid":
+      return colorPalette.danger;
+    default:
+      return colorPalette.neutral;
+  }
+};

frontend/editor/src/core/hooks/tools/validateSignature/utils/signatureStatus.ts

@@ -1,6 +1,5 @@
 import type { TFunction } from "i18next";
 import type { SignatureValidationSignature } from "@app/types/validateSignature";
-import { colorPalette } from "@app/hooks/tools/validateSignature/utils/pdfPalette";
 
 export type SignatureStatusKind = "valid" | "warning" | "invalid" | "neutral";
 
@@ -131,16 +130,3 @@ export const computeSignatureStatus = (
     details: issues,
   };
 };
-
-export const statusKindToPdfColor = (kind: SignatureStatusKind) => {
-  switch (kind) {
-    case "valid":
-      return colorPalette.success;
-    case "warning":
-      return colorPalette.warning;
-    case "invalid":
-      return colorPalette.danger;
-    default:
-      return colorPalette.neutral;
-  }
-};