Implement screen validation

[OCopping]

When a file is saved in Phoebus, a comment gets added to the top to say it was saved:

<?xml version="1.0" encoding="UTF-8"?>
<!--Saved on 2025-11-18 15:23:29 by ryi58813-->
<display version="2.0.0">
  <name>Synoptic</name>

This can be used to determine if a file needs to be validate or completely re-generated.

[codecov]

Codecov Report

❌ Patch coverage is 71.96262% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.43%. Comparing base (5ab1098) to head (c4bf483).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
src/techui_builder/utils.py	26.66%	11 Missing ⚠️
src/techui_builder/builder.py	67.74%	10 Missing ⚠️
src/techui_builder/autofill.py	33.33%	6 Missing ⚠️
src/techui_builder/__main__.py	0.00%	1 Missing ⚠️
src/techui_builder/generate.py	92.30%	1 Missing ⚠️
src/techui_builder/validator.py	97.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
- Coverage   81.83%   81.43%   -0.41%     
==========================================
  Files           7        9       +2     
  Lines         578      657      +79     
==========================================
+ Hits          473      535      +62     
- Misses        105      122      +17     

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[OCopping]

I attempted adding a custom comment in alongside the "Saved on" comment and it got overwritten/deleted on a subsequent save of the bob screen in phoebus.