fix: missing Union import, hardcoded extension, multi-page index reset, Ollama timeout

[vidhip222]

Description:

Four bug fixes across the PDF filling pipeline and LLM integration layer.

1. src/main.py: Add missing Union import (Fixes [BUG]: Make exec fails because Union is not imported in src/main.py #274)
   run_pdf_fill_process used Union[str, os.PathLike] in its type annotation but Union was never imported, causing a NameError on any call to this function.

2. src/filler.py: Replace hardcoded extension slicing (Fixes [BUG]: Hard-coded extension assumption breaks filename generation #247)
   pdf_form[:-4] silently assumed a 4-character .pdf extension, producing corrupted output filenames for any other extension. Replaced with os.path.splitext() which correctly handles any file extension.

3. src/filler.py: Fix multi-page PDF field index reset (Fixes [BUG]: Multi-page PDF filling resets answer index and misaligns fields #238)
   The answer index i was initialised inside the page loop, resetting to 0 on every page. Fields on pages 2+ were incorrectly filled with values already used on page 1. Moved i outside the loop so it advances continuously across all pages.

4. src/llm.py: Add timeout to Ollama requests (Fixes [BUG]: Ollama request path lacks timeout and robust error handling #228)
   requests.post() had no timeout, causing the server to hang indefinitely if Ollama was slow or unresponsive. Added a 60-second timeout and a dedicated Timeout exception handler with a descriptive error message.

Issues:

Fixes #274
Fixes #247
Fixes #238
Fixes #228

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Verified os.path.splitext() produces correct filenames for .pdf inputs
• Verified answer index advances correctly across multi-page PDFs
• Verified Union import resolves the NameError in run_pdf_fill_process
• Verified timeout=60 and Timeout handler surface a clear error instead of hanging

Test Configuration:

• Python: 3.x
• OS: Windows 11

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes