fix(lint): switch Vault.delete() to FileManager.trashFile()

ObsidianReviewBot's `prefer-file-manager-trash-file` is the optional
finding it surfaces against image-gin: `Vault.delete()` ignores the
user's "Files & links → Move to system trash / Obsidian trash / delete
permanently" preference, while `FileManager.trashFile()` respects it.

Three sites, all behind explicit user actions (settings toggle or
the Clear Cache button), so the deletion-preference is exactly the
contract we want to honor.

- BatchDirectoryConvertLocalToRemote.ts:449 — local file removal
  after a successful ImageKit upload, gated by
  `imageKit.removeLocalFiles` setting.
- imageCacheService.ts:156, 164 — `clearCache()` removing the
  configured cache folder (either as a single TFile or as the
  contents of a folder).

After this commit `pnpm exec eslint .` reports 0 errors and 0
warnings against the obsidianmd recommended config.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/modals/BatchDirectoryConvertLocalToRemote.ts

@@ -446,7 +446,7 @@ export class BatchDirectoryConvertLocalToRemote extends Modal {
         // Optionally remove local file if setting is enabled
         if (this.plugin.settings.imageKit.removeLocalFiles) {
             try {
-                await this.app.vault.delete(imageFile);
+                await this.app.fileManager.trashFile(imageFile);
             } catch (error) {
                 logger.warn(`Could not delete local file ${imageRef.imagePath}:`, error);
             }

src/services/imageCacheService.ts

@@ -153,7 +153,7 @@ export class ImageCacheService {
             const cacheFolder = this.app.vault.getAbstractFileByPath(this.cacheFolder);
             if (cacheFolder && cacheFolder instanceof TFile) {
                 // If it's a file, delete it
-                await this.app.vault.delete(cacheFolder);
+                await this.app.fileManager.trashFile(cacheFolder);
             } else if (cacheFolder) {
                 // If it's a folder, delete all files in it
                 const files = this.app.vault.getFiles().filter(file => 
@@ -161,7 +161,7 @@ export class ImageCacheService {
                 );
                 
                 for (const file of files) {
-                    await this.app.vault.delete(file);
+                    await this.app.fileManager.trashFile(file);
                 }
             }