LT-22524: Add substring search to Find Lexical Entry

[thejambi]

Quick Summary

Find Lexical Entry now matches typed characters anywhere in a word for queries of 3+ characters, using liblcm's new SearchType.Substring; shorter queries keep the original full-text search. The mode decision lives in a unit-tested SubstringSearchPolicy, and results retain the existing exact -> starts-with -> anywhere ordering.

Depends on sillsdev/liblcm#395

https://jira.sil.org/browse/LT-22524

CI-ready checklist

• Commit messages follow .github/commit-guidelines.md (subject ≤ 72 chars, no trailing punctuation; if body present, blank line then ≤ 80-char lines).
• No whitespace warnings locally:

  git fetch origin
  git log --check --pretty=format:"---% h% s" origin/<base>..
  git diff --check --cached

• Builds/tests pass locally (or I've run the CI-style build via Bash script or MSBuild).
• If this is core-developer AI-assisted work, I followed Docs/workflows/ai-pr-workflow.md and ran pr-preflight or the equivalent branch-readiness review before requesting review.
• For any Src/** folders touched, corresponding AGENTS.md files are updated or explicitly confirmed still accurate.

Notes for reviewers (optional)

---

This change is 

[github-actions]

Comment hygiene (advisory)

No comment-style violations in the lines this branch adds since origin/main.

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   10m 57s ⏱️ +5s
5 869 tests +8  5 788 ✅ +8  81 💤 ±0  0 ❌ ±0 
5 878 runs  +8  5 797 ✅ +8  81 💤 ±0  0 ❌ ±0 

Results for commit f30f2a4. ± Comparison against base commit b8f5463.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 16.66667% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.35%. Comparing base (b8f5463) to head (f30f2a4).

Files with missing lines	Patch %	Lines
Src/LexText/LexTextControls/EntryGoDlg.cs	0.00%	15 Missing and 1 partial ⚠️
...Common/Controls/XMLViews/MatchingObjectsBrowser.cs	0.00%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1069   +/-   ##
=======================================
  Coverage   38.35%   38.35%           
=======================================
  Files        1507     1508    +1     
  Lines      350617   350644   +27     
  Branches    40298    40302    +4     
=======================================
+ Hits       134471   134491   +20     
- Misses     186916   186920    +4     
- Partials    29230    29233    +3     

Files with missing lines	Coverage Δ
Src/LexText/LexTextControls/EntryGoSearchEngine.cs	46.55% <100.00%> (ø)
...c/LexText/LexTextControls/SubstringSearchPolicy.cs	100.00% <100.00%> (ø)
...Common/Controls/XMLViews/MatchingObjectsBrowser.cs	0.47% <0.00%> (-0.03%)	⬇️
Src/LexText/LexTextControls/EntryGoDlg.cs	0.00% <0.00%> (ø)

... and 3 files with indirect coverage changes

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