Recognize typed function names in the editor

[Happypig375]

Summary

• recognize complete typed function names and replace them with the dedicated operator atom
• keep recognition bounded so substrings of longer identifiers are not rewritten
• retain lightweight provenance so Left/Right, insertion, and Backspace can expand a recognized function back to editable letters
• cover nested lists and ambiguous edit paths

Fixes #83.

Validation

• KeyPressTests: 258/258 passed
• Core test project build passed
• all GitHub build, format, benchmark, and platform checks passed

Compatibility and maintenance cost

The change adds editor recognition/provenance logic but does not alter the LaTeX parser or public API. Recognition is limited to the issue's named function set.

Review

No formal GitHub review is recorded yet; CI is fully green.