docs(javadoc): make document.* public API doclint-clean

[DemchaAV]

What

Makes the entire public canonical surface com.demcha.compose.document.*
Javadoc doclint-clean — mvn javadoc:javadoc -pl . (doclint=all,
failOnError=true, show=public) now runs warning-free.

Why this is bigger than it looked

The work started from "~100 no @return warnings on CvTheme factories."
That count was an artifact of javadoc's default -Xmaxwarns=100 cap —
the log literally stopped at 100 warnings. Raising the cap revealed the
true surface:

Warning	Count
no @param	471
no @return	191
no comment (public element, zero Javadoc)	205
no main description	35
use of default constructor	16
@deprecated in package-info	9
no @throws	2
Total	929 across 142 files / 28 packages

The build was green before (warnings, not errors), and stays green — this
just closes the real gaps on the public docs surface.

What changed

Additive Javadoc only, with two sanctioned, behaviour-neutral exceptions:

• 16 explicit no-arg constructors in layout/definitions/* — each
  documents the otherwise-synthesised public default constructor (byte-identical
  behaviour). This is the repo's own idiom for doclint's use of default constructor (cf. PdfTableRowFragmentRenderHandler()).
• Removed the @deprecated block-tag from 9 package-info.java files —
  doclint forbids that tag in package docs; the @Deprecated(...) annotation
  and the prose body already carry the deprecation notice. @since and the
  annotation are untouched.

No public API, signature, or runtime behaviour change. Every @param on a
convenience constructor was copied from the documented primary
constructor/record header in the same file, so wording stays consistent.

Verification

• mvn javadoc:javadoc -pl . — 0 warnings under doclint=all (confirmed
  both with the cap temporarily raised and again under the unmodified CI config).
• mvn test -pl . — 1060 tests, 0 failures, 0 errors.
• Diff is 142 files under document.* (+ this CHANGELOG note); 0 code lines
  deleted — all diff-deletions are Javadoc comment reflows.

Scope note

The original ask framed this as a small docs(templates) @return/@param
pass. Given the cap discovery (929, spanning the whole document.* surface and
including ~256 elements needing real descriptions), the decision was to go for
full warning-clean rather than a partial pass. CHANGELOG v1.6.9 updated
under Documentation.