fix(showcase): resolve every card's View-Code link and curate its copy

[DemchaAV]

Why

30 of the 85 showcase cards point their "View Code" link at a path that 404s.
26 examples were never registered in ShowcaseMetadata, so the manifest fell
back to the examples-root URL with a filename-derived title and a generic
"Generated showcase for …" description. 4 more (debug-overlay, block-align,
svg-icon-gallery, vector-path) resolved through the feature() /
flagship() group→class switch to the wrong or a non-existent class — the
switch guessed the class from the group, which cannot hold once a group has one
class per id (layout, navigation, text, …).

What

• feature() / flagship() now take the example class explicitly, like cv()
  / letter() — the brittle group→class switch is gone.
• Registered the 26 missing examples (in-document navigation, colour emoji,
  inline runs, per-page layout, charts, multi-section, the engine-deck /
  feature-catalog / financial-report flagships, …) each with a curated title, a
  one-line description naming the concrete DSL API it demonstrates, and tags.
• Pointed the 4 mis-resolved links at their real class.
• groupLabel: added charts / navigation / structure / title / docx.
• Regenerated web/examples.json: exactly those 30 entries change, the other 55
  stay byte-identical, links preserved at /blob/v1.9.0.

Tests

• Examples module compiles (ShowcaseSync BUILD SUCCESS).
• Every code URL in web/examples.json (85/85) resolves to a committed
  .java file.
• A structured diff confirms exactly the 30 intended entries changed (4
  link-only, 26 link + curated copy); the cited DSL APIs were each grepped in
  their example source.

Relation / deploy

Independent of #267 (which ships the 32 missing preview PDFs); this one fixes
the View-Code links and card copy. Both reach the live site the same way: once
merged to develop, a main fast-forward + deploy-web (asset-only, no version
bump, no tag).