#2694 Docs: update the model validate Expression paths example in cel-expressions.md

swamp-club#2493 changes how swamp model validate lays out a failed Expression paths check in log mode. The example in content/manual/reference/cel-expressions.md (the block under the list of malformed-template forms) shows the old, misaligned output, where the first entry is glued to the arrow.

Replace it with the new layout: one arrow per failed expression, its details indented under it, and the shared fix for another service's template syntax printed once after the list.

✗ Expression paths
  → {{self.name}}
    Expression uses {{...}} instead of ${{...}} at "[HOST-1]"
    Add "$" prefix: ${{...}}.
  If this is another service's template syntax, build it with CEL string concatenation, e.g. ${{ "{" + "{name}" + "}" }}, or have the model type declare the field with .meta({ foreignTemplate: true }).

In --json output, a failed Expression paths item now also carries an expressionErrors array (expression, error, suggestion, remedy, availableKeys), which the reference could mention.