Frontpage portal blocks + Seimas membership views & XSLT overrides

[namedgraph]

What

Two related strands of work on the end-user LinkedDataHub app.

1. Frontpage portal (app/root.ttl)

Turns the LDH root document from a bare container listing into an introduced,
data-driven portal that visualises the main datasets and leads navigation into
key subpages. Ordered content blocks (rdf:_1 … rdf:_11):

1. Mission intro (ldh:XHTML) + links to the SPARQL spec and EXAMPLES.md
   2–3. Apskritys — ldh:View / GridMode grid of the 10 top-level admin units
   (counties, cv:level atu:LTU_APS), rendered as coat-of-arms cards that drill
   into the :SubUnits view
   4–5. Frakcijų dydžiai — bar chart, current members per faction
   6–7. Seimo narius iškėlusios partijos — ldh:View / TableMode listing the
   nominating parties, clickable to their pages (previously a "members per party"
   bar chart)
   8–9. Komitetų ir komisijų pirmininkai — ldh:View / TableMode listing the
   current chair persons
2. "Naršyti duomenų rinkinius" prompt
3. #select-children — the container listing, kept last

2. Seimas membership views + client-side XSLT overrides

• app/ns.ttl — 1:N inverse views (current/former members, units, nominated
  members, memberships), targeted by discriminating rdfs:range types.
• etl/seimas/mappings/persons.rq + regenerated
  datasets/current/seimas/persons.trig — org:Membership /
  org:memberDuring intervals carrying a dct:title period label
  (e.g. "2024-11-14 – dabar") so the memberships table can show a readable period.
• etl/shapes/seimas.ttl — matching SHACL shape updates.
• files/overrides.xsl, client.xsl, layout.xsl + Makefile sef target +
  docker-compose.yml mounts + .gitignore + CLAUDE.md docs — end-user Saxon-JS
  XSLT overrides that tidy the memberships table and suppress the n-ary membership
  plumbing blocks. The compiled SEF (files/client.xsl.sef.json) and
  docker-compose.override.yml stay gitignored.

Notes

• Embedded frontpage queries use the FROM <urn:x-arq:UnionGraph> cross-graph
  style and are base-agnostic (no hardcoded local URIs), so the committed root
  document works on any deployment base.
• Views project a single entity type: LDH renders a view by DESCRIBE-ing the
  projected IRIs, so projecting label literals or several resource types yields an
  empty / muddled result. This is also why the parties block is a plain list — a
  DESCRIBE view can't render the aggregate member counts the old chart showed.
• GridMode vs TableMode: counties carry foaf:depiction (coats of arms) → grid
  of thumbnail cards; parties have only a label → table.
• The view blocks require the LinkedDataHub change that hoists the FROM clause
  when wrapping a view SELECT into DESCRIBE (otherwise the view returns 400).
  The faction bar chart renders without it.

Verification

• riot --validate app/root.ttl passes; all embedded queries run green against a
  live deployment (10 counties, each with a depiction; 11 nominating parties).
• Deployed via make install; the served root document confirms the block order,
  the GridMode/TableMode wiring, and removal of the old parties chart.

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