Add UDQ/ACTIONX support: recognition, highlighting, hover, completion, alignment

[magnesj]

Summary

Brings the UDQ expression sub-language and ACTIONX action blocks into the editor.

Recognition & diagnostics

• Validate that every statement in a UDQ block begins with a control word
  (ASSIGN/DEFINE/UNITS/UPDATE); flag stray leading tokens. Continuation
  lines of a statement whose / is deferred are not flagged.
• Track ACTIONX ... ENDACTIO blocks and flag an action block that is never
  closed by a matching ENDACTIO.

Highlighting (tmLanguage)

• Scope UDQ control words, UDQ functions (name-followed-by-paren), and the
  comparison/logical operators used in expressions.
• Scope the ACTIONX / ENDACTIO action-block delimiters as control keywords.

Editor (hover & completion)

• Hover on a UDQ control word or function shows its meaning/signature.
• Completion inside UDQ/ACTIONX offers control words at statement start and
  UDQ functions (inserted with parentheses) inside expressions.

Column alignment

• UDQ expression blocks get a dedicated three-column layout — control word,
  variable, and expression — that lines up each statement's terminating / and
  treats a / used for division inside the expression as part of the
  expression rather than the terminator.
• Interspersed comments and blank lines inside a UDQ table no longer break the
  alignment groups.

Docs

• README feature, diagnostics, and release-notes entries for the above.

Refs #18

Verified: tsc clean; 314 jest tests pass (9 suites).