#2402 Docs: CEL expressions manual page - document DataRecord.path and point model.*.file at data.latest().path

Follow-up to swamp-club#2288 (swamp PR pending on branch fix/2288-data-record-path).

What changed

Data records returned by the CEL data.* functions (data.latest, data.version, data.findBySpec, data.findByTag, data.query) gain a path field: the local filesystem path of the version's stored file. It replaces the deprecated model.<name>.file.<specName>.<instanceName>.path.

Pages to update

content/manual/reference/cel-expressions.md:

1. The DataRecord field table (the one listing size as the content size in bytes) needs a path row: string, local path of the stored content file; empty string for ephemeral data, records from another namespace in a shared datastore, or a file that cannot be made local.
2. The deprecated model.<name>.file.<specName>.<instanceName> section should point readers at data.latest(model, instance).path, with an example such as a shell run argument that passes the path to wc -l.
3. Worth noting:
   • On a lazy-hydration datastore, data.latest() / data.version() download the file first; list lookups do not.
   • The path is on the host that evaluates the expression (not a remote worker).
   • swamp data query and the serve API always return an empty path.
   • Select .path rather than passing the whole record into an input.