Duplicate navbarDropdown IDs Break Dropdown Menus

[keraattin]

Bug Description
The generated HTML report contains four elements sharing id="navbarDropdown" — one per navigation section. Duplicate IDs are invalid HTML and cause Bootstrap's JavaScript to bind dropdown behavior only to the first match, leaving the Links, Attachments, and Digests dropdowns non-functional in some browsers.

Expected Behavior or Results
Each navbar dropdown should have a unique ID so all four menus open correctly.

Reproduce Steps

1. Run python3 email-analyzer.py -f sample.eml -o report.html
2. Open report.html in a browser
3. Click the Links, Attachments, or Digests navbar items — they may not open
4. Inspect the HTML source and find four elements with id="navbarDropdown"

Desktop (please complete the following information):

• OS with Version: Any
• Python Version: Python 3.10+
• Browser with Version: Firefox / Chrome (behavior varies)
• EmailAnalyzer Project Version: v2.0

Additional context
Affected code - html_generator.py lines 276, 284, 293, 303:

<a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" ...>

Fix: use unique IDs like id="headersDropdown", id="linksDropdown", id="attachmentsDropdown", id="digestsDropdown" with matching aria-labelledby attributes.