refactor: Refactor autofill use registry

[OCopping]

Summary

Updates the autofiller to support entity registry fallback, allowing widget names in index.bob to match
either techui.yaml components or individual entity PVs from the registry.

Depends on PR #276 (refactor-builder-registry).

Changes

• autofill.py — Added entities parameter to Autofiller; _autofill_from_path() falls back to entity registry when widget not in gui_components; replace_content() handles Component | Entity
• main_app.py — Pass gui.entities to Autofiller
• tests/test_autofiller.py — Updated tests for entity fallback and priority; new tests for replace_content() with Entity
• tests/conftest.py — New autofiller_index_trees, autofiller, and autofiller_with_entities fixtures

[codecov]

Codecov Report

❌ Patch coverage is 95.77465% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.29%. Comparing base (2dd3dc6) to head (c2811e2).

Files with missing lines	Patch %	Lines
src/techui_builder/generate.py	91.30%	2 Missing ⚠️
src/techui_builder/builder.py	96.55%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
- Coverage   96.55%   96.29%   -0.27%     
==========================================
  Files          17       17              
  Lines        1075     1106      +31     
==========================================
+ Hits         1038     1065      +27     
- Misses         37       41       +4     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.