feat: add O-spec sub-type support for fixed-format column assist

[bobcozzi]

Summary

This PR adds correct column ruler and Column Assistant support for all Output (O) spec line types in fixed-format RPGLE. It supersedes #507 (@supravi96) which was a good idea but had incorrect column positions and was missing sub-type detection logic.

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What was wrong with #507

• The O-spec column positions were off — the definitions didn't match the actual fixed-format column layout
• A single O-spec entry was used for all O-spec lines, but the ILE O-spec actually has five structurally distinct line types, each with different fields at different positions

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O-spec line types

Fixed-format Output specs have five distinct line layouts. This PR adds a SpecRulers entry and full SpecFieldDef array for each:

Key	Description	Distinguishing characteristic
O	File/Record header line	Has filename (cols 7–16) and/or record type (col 17)
OAnd	AND/OR continuation line	Cols 16–20 contain AND or OR
OF	Field output line	Has an end position (cols 47–51) alongside a field name or constant
OFC	Constant-only line	No field name; constant/edit word starts at col 53
OXF	Field-name-only line	Has a field name but no end position

Updated Rulers

Each sub-type gets its own reference ruler that reflects only the fields relevant to that line:

O    : .....OFilename++DF..N01N02N03Excnam++++B++A++Sb+Sa+.Constant/Editword/DateFormat
OAnd : .....O.........And++N01N02N03ExceptName+++++++++++++++++++++++++++++++++++++++++
OF   : .....O..............N01N02N03FieldName+++++BEcEndPoDConstant/Editword+++++++++++
OFC  : .....O..................................................Constant/Editword+++++++++++
OXF  : .....O..............N01N02N03FieldName++++++B+++++++++++++++++++++++++++++++++++

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How sub-type detection works

A new resolveSpecKey(line) function in columnAssist.ts inspects the content of the current line to determine which O-spec sub-type it is, and returns the appropriate key for specs and SpecRulers lookup:

function resolveSpecKey(line: string): string {
  const specLetter = line[5]?.toUpperCase() ?? ``;
  if (specLetter !== `O`) return specLetter;

  const paddedLine = line.padEnd(80);
  const andOrKeyword = paddedLine.substring(15, 20).trim().toUpperCase();
  if (andOrKeyword === `AND` || andOrKeyword === `OR`) return `OAnd`;

  const filename  = paddedLine.substring(6,  16).trim();
  const type      = paddedLine.substring(16, 17).trim();
  const fieldName = paddedLine.substring(29, 43).trim();
  const endPos    = paddedLine.substring(46, 51).trim();
  const constant  = paddedLine.substring(52).trim();

  if (endPos && (fieldName || constant)) return `OF`;
  if (filename || type)                  return `O`;
  if (!fieldName && constant)            return `OFC`;
  if (fieldName)                         return `OXF`;
  return `O`;
}

This is called from both getAreasForLine (ruler decoration) and promptLine (Column Assistant UI), so both the visual ruler and the interactive field editor show the correct fields for whichever O-spec line type the cursor is on.

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Files changed

• extension/client/src/schemas/specs.ts — added SpecRulers entries and SpecFieldDef arrays for O, OAnd, OF, OFC, OXF
• extension/client/src/language/columnAssist.ts — added resolveSpecKey(), updated getAreasForLine and promptLine to use it

Closes #507