Fix v1.9.0 logo upload and add MiKTeX PATH support

This commit fixes the logo upload issue and adds MiKTeX to the app's PATH for LaTeX/PDF support.
**Logo Upload Fix:**
- Replaced file input with Browse button that uses dialog.showOpenDialog
- Added browse-header-footer-logo IPC handler in main process
- Now gets reliable file paths without depending on file.path property
- Added browse-btn CSS styling
**MiKTeX PATH Addition:**
- Automatically adds MiKTeX bin directory to process.env.PATH on Windows
- Enables XeLaTeX/PDFLaTeX for PDF exports with headers/footers
- Logs PATH addition for debugging
**Files Changed:**
- src/main.js: Added MiKTeX PATH setup, browse logo IPC handler
- src/renderer.js: Changed to browseForLogo() function, updated event listeners
- src/index.html: Replaced file inputs with browse buttons
- src/styles.css: Added .browse-btn styling
**Testing Notes:**
- Logo upload now works without "path undefined" errors
- DOCX exports with headers/footers confirmed working
- PDF exports should now use Pandoc+XeLaTeX with MiKTeX in PATH
- Requires MiKTeX installation and PC restart for full functionality
🤖 Generated with [Claude Code](https://claude.com/claude-code)

src/index.html

@@ -964,7 +964,7 @@
                             </div>
                             <div class="hf-logo-row">
                                 <label>Header Logo/Image:</label>
-                                <input type="file" id="header-logo" accept="image/*">
+                                <button id="header-logo-browse" class="browse-btn">Browse...</button>
                                 <button id="header-logo-clear" class="clear-btn">Clear</button>
                                 <span id="header-logo-preview" class="logo-preview"></span>
                             </div>
@@ -992,7 +992,7 @@
                             </div>
                             <div class="hf-logo-row">
                                 <label>Footer Logo/Image:</label>
-                                <input type="file" id="footer-logo" accept="image/*">
+                                <button id="footer-logo-browse" class="browse-btn">Browse...</button>
                                 <button id="footer-logo-clear" class="clear-btn">Clear</button>
                                 <span id="footer-logo-preview" class="logo-preview"></span>
                             </div>