feat: Rework Autofiller to support navtab-based multi-file bob structures

[OCopping]

Previously, the autofiller only handled a single index.bob file. This change enables it to:

• Discover and autofill multiple .bob files matching index[-<suffix>].bob (or a specified <filename>[-<suffix>].bob)
• Detect navtabs widgets in index files and recursively autofill the tab screen files they reference
• Move _get_nav_tabs into utils.py for reuse across modules

Files changed:

• autofill.py — Major refactor: Autofiller now manages multiple index trees and traverses navtab links
• main_app.py — Updated find_bob() → find_index_bobs() to return a base path + list of related .bob files
• utils.py — Exported _get_nav_tabs helper

Tests updated:

• test_autofiller.py — New tests for navtab autofill behavior
• test_cli.py — Adapted for new multi-file discovery

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.54%. Comparing base (b3f1f06) to head (56de030).

Files with missing lines	Patch %	Lines
src/techui_builder/autofill.py	94.23%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #267      +/-   ##
==========================================
- Coverage   96.61%   96.54%   -0.07%     
==========================================
  Files          17       17              
  Lines        1033     1072      +39     
==========================================
+ Hits          998     1035      +37     
- Misses         35       37       +2     

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