feat(rendering): add generate_heex clauses for 5 shell-primitive kinds

[ty13r]

Summary

Adds IUR fallback generate_heex clauses for five canonical kinds that currently render as empty <div> shells in force_fallback: true mode (operator_v2 Phase 2 + Wave C). This is documented as Substrate Gap #1 in ariston-ui/docs/operator-v2-phase-2-deferred-findings.md.

Tier 2 substrate gap proposal - opens as DRAFT for Pascal review. These are not new canonical primitives (all five already have LiveUi.Renderer clauses on the force_fallback: false path), but adding the IUR fallback path affects every consumer of force_fallback: true mode. Markup, class, and aria decisions need Pascal sign-off before merge.

Context

LiveUIAdapter.render(force_fallback: true) routes through generate_heex/2 clauses. The five kinds below had LiveUi.Renderer clauses (the normal runtime path) but no generate_heex clauses, so they fell through to the default empty-shell catch-all. ariston-ui works around this today by substituting alternative kinds with coverage (e.g., sticky_frosted_header for top_strip). Once Pascal approves this PR, those substitutions can be removed.

Per-kind decision matrix

Kind	Wrapper element	Class prefix	Key IUR props read	Children
top_strip	<header>	ash-top-strip	title (h2), brand (span), context (span)	yes - via generate_children/2
sidebar_section	<section>	ash-sidebar-section	label (h3), action_label/action_glyph (button text), action_intent (boolean to show action button)	yes - via generate_children/2
sidebar_item	<li>	ash-sidebar-item	label (button text), selected?/selected (aria-current="page" + --selected modifier class)	yes - nested inside <button>
tabs	<div>	ash-tabs	items (list of %{"id" => ..., "label" => ...}), active_item_id (string matched against item id for aria-selected)	no - tab items are inline buttons in a role=tablist div
tree_view	<section>	ash-tree-view	nodes (list), selection_mode (data attr)	no - nodes rendered by existing render_tree_nodes/1 helper

Open questions for Pascal

1. top_strip: Is data-live-ui-shell-position="top" the right data-attr to carry through the IUR fallback, or is it handled by the layout shell and unnecessary on the <header> directly?
2. sidebar_item: LiveUi.Renderer wraps children inside the <button> element. Is that correct or should children be siblings of the button?
3. tabs: The IUR fallback renders tab items as inline <button type="button" role="tab"> (no patch/navigate targets, since IUR props don't carry routing info). Acceptable for the fallback path?
4. tree_view: The fallback delegates to the existing render_tree_nodes/1 helper (which reads label/title/name/value but not selected?/expanded?). Should I extend that helper to carry those props, or is the current behavior sufficient for fallback mode?
5. CSS class convention: All clauses use ash-* prefix per existing convention (LiveUi.Renderer uses live-ui-*). Please confirm ash-* is correct for the IUR fallback path.

Test plan

Quality-gate commands run from /tmp/ash-ui-gap-1 (worktree of ash_ui at claude/generate-heex-shell-primitives):

• mix format --check-formatted lib/... test/... - PASS
• MIX_ENV=test mix compile --warnings-as-errors - PASS (Generated ash_ui app)
• MIX_ENV=test mix test test/ash_ui/rendering/live_ui_adapter_test.exs - PASS (45 tests, 0 failures, 37 existing + 8 new)

New tests verify: wrapper element + class present, key text props rendered, children propagated, aria-current="page" on selected sidebar_item, --selected modifier class, action button conditional on action_intent, aria-selected="true" on active tab item.

🤖 Generated with Claude Code

[ty13r]

Cross-linking the three operator_v2 substrate-gap items (per project-ariston Update 8):

• feat(authoring): allow list_item_multi_column on repeat-bound elements #142 — Gap 2: @list_widgets allowlist (Tier 1 mechanical)
• This PR (feat(rendering): add generate_heex clauses for 5 shell-primitive kinds #144) — Gap 1: generate_heex clauses for 5 shell-primitive kinds (Tier 2 DRAFT)
• Authority.create/2: support explicit :name opt for screen lookup #143 — Gap 3: Authority.create/2 name vs lookup mismatch (Tier 2/3 issue, direction-pick)