feat(reativa): implement every remaining example — full parity with Xote

[brnrdog]

Summary

Brings @prescriptive/reativa (OCaml + Melange) from 37 example implementations to full parity with @prescriptive/xote — every spec that has a Xote demo in website/src/Examples.res now has a matching Reativa preview, so the site can show the two implementations side by side for the whole catalogue.

Delivered in three reviewable commits (52 new example implementations):

Batch	Count	Specs
One	20	elements label legend logo typography; components breadcrumb button-group card empty-state footer input-group list pagination stat toolbar; blocks cta-section faq feature-grid hero pricing-table testimonial
Two	20	overlays/menus alert-dialog dropdown-menu context-menu popover hover-card sheet drawer toast; data/pickers table data-table chart carousel combobox command calendar date-picker; nav navbar menubar navigation-menu sidebar
Three	12	components form resizable search comment; pages dashboard landing-page pricing settings sign-in; flows authentication checkout onboarding

reativa now covers 26 elements, 42 components, 13 blocks, 5 pages, and 3 flows.

Approach

• Each example mirrors its Xote twin exactly, composed over Reativa.View and reusing the existing components (Button, Badge, Avatar, Icon, IconButton, Separator, Input, Link, Backdrop, Switch, Field), styled against @prescriptive/tokens so a re-theme cascades through both implementations identically.
• Added to Registry.mlx as inline *_example functions wired into example_for / example_ids (the ES surface the website consumes) — matching how the existing reativa examples and the Xote Examples.res modules are structured. No website code change needed; the Reativa tab is driven by example_ids from the bundle.
• A small el helper wraps View.element for pure-structure demos so uncommon tags (table, h1, blockquote, nav, …) never depend on which JSX tag helpers the mlx layer exposes, plus a contains_ci substring helper for the filterable demos.

Reactive primitives used

View.show for the open/closed overlays (dismissed via Backdrop), View.for_ for the live-filtered lists (combobox, command, search, data-table), class_reactive for selected-day / active-dot state (calendar, date-picker, carousel), reactive style for the carousel track and resizable panels, View.On.on for the contextmenu / mouseenter / mouseleave / focus events, and View.On.submit + prevent_default for form.

Verification

• API used was checked directly against the reativa source at the pinned build commit (c94697df), not from memory — confirmed View.for_, View.On.on, the polymorphic 'a value (for the reactive checked binding), and the tag/attr/event surface.
• example_for match arms and example_ids were cross-checked to match exactly (89 = 89, both directions), catch-all last.
• The only Xote demo ids left uncovered are account and password, which are not specs (no .md under specs/) and so never surface a Reativa tab — intentionally omitted.

⚠️ Not compiled locally: the melange build needs an opam/melange/mlx toolchain that isn't available in this environment, so I relied on the source-verified API plus review. CI compiles the reativa bundle, so this PR will exercise the real build. The checked-in website/src/reativa.bundle.js refreshes when CI rebuilds it.

Each batch adds a Changeset (@prescriptive/reativa minor).

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https://claude.ai/code/session_012DYiHqv5HaSufQ5JH7Mokh

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