feat(cli): colorized, columnized text output with line:col locations

Replace the per-line fmt.Println loop with writeTextFindings() in
cmd/glint/output.go. The new renderer:

- Aligns all findings into four space-separated columns: location,
  rule ID, severity, message — widths computed from the full finding
  set so all lines are flush
- Colors severity words when stdout is a TTY and NO_COLOR is not set:
  red+bold for "error", orange+bold for "warning"; location dimmed;
  rule ID bold
- Formats location as file:line:col when column is known, file:line
  otherwise, falling back to just file

To populate column numbers, add Column int to model.Job (set from
keyNode.Column in the YAML parser) and Finding.Column (set during
the checkJob source-location attachment pass and in the ten cross-job
check sites that explicitly set Line: job.Line).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/linter/variables.go

@@ -148,6 +148,7 @@ func checkVariableRefs(p *model.Pipeline) []Finding {
 					Job:      name,
 					File:     job.File,
 					Line:     job.Line,
+					Column:   job.Column,
 					Message:  fmt.Sprintf("rules[%d].if: $%s is not declared in pipeline or job variables:", i, varName),
 				})
 			}