intent: duplicable defaults take now on a timestamp field (#7396)

[delchev]

IntentParser.validateDuplicableDefault accepted now on a date / month / week
field and refused everything else, so

duplicable:
  defaults: { recordedAt: now }   # recordedAt is `type: timestamp`

failed validation with "that property is not a date" - although a timestamp
property holds exactly the kind of value now means. date and timestamp
differ only in precision, and the copy of a document is made now in both cases,
so the refusal ruled out the one value an author would write there and left a
calculatedActionOnCreate class, or a clone carrying the source's timestamp, as
the only ways to say it.

The sibling of #7392 on the duplicable path, and one rendering step further than
it, because this half renders in JavaScript rather than Java:

• validateDuplicableDefault reads the accepted types from a named set, so a
  temporal type added later is one line and not another equals chain;
• EdmIntentGenerator.duplicateDefaults emits the AUTHORED shape instead of
  collapsing everything that is not month/week to date;
• todayAs in document-page.js.template renders a timestamp as the ISO
  instant - the same conversion the form's own toPayload() already does for a
  datetime input, since a java.time.Instant property does not bind the local
  calendar shapes the other kinds send. The calendar shapes stay built from the
  LOCAL fields: east of Greenwich toISOString() dates an evening copy
  yesterday, which is why the timestamp shape is the deliberate exception and
  not a relaxation of that rule.

A model that declares no timestamp default generates byte-identically.

Verified: DuplicableIntentTest accepts now on a timestamp field and still
refuses it on a string and on a to-one relation (whose default assigns a raw
foreign key), 20 tests green; EdmIntentGeneratorTest asserts the emitted
shape: timestamp next to the unchanged date / month / literal entries; the
engine-intent unit suite is green (1327 tests); IntentEmissionCoverageIT now
carries a timestamp field on Reorder with a now default and asserts both
the generated todayAs('timestamp') assignment and the helper's instant branch
in the published document page - green, and the module it publishes compiles.
Not run: the full IT suite, and no browser pass on a real Duplicate click.

Fixes #7396

🤖 Generated with Claude Code