feat: gallery + generic blueprint viewer, add Grid blueprint

Refactor the List-specific screen into a data-driven, reusable viewer:
- generic Blueprint type + shared LoadState machine + registry
- vue-router: / (gallery) and /b/:slug (illustration)
- BlueprintViewer renders any blueprint; specimens stay bespoke
- add Grid blueprint (6 functions incl. Position) + GridSpecimen

CONTEXT.md

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+# Context — ubiquitous language
+
+The shared vocabulary for `blueprints`. These terms should appear verbatim in
+conversation, code, file names, and commits. This file is a glossary only — no
+implementation details (those live in `DESIGN.md`).
+
+## Blueprint
+
+A named contract for a recurring UI pattern, taken from the `blueprint-ontology`
+repo — declarative, categorical, abstract (a _concept_ in Jackson's sense). It
+defines what must be true of the pattern: its signature, state machine, behaviors,
+invariants, functions, critical-performance thresholds, and failure modes. Examples:
+`List`, `Grid`, `Table`, `Async`.
+
+Blueprints come in two roles (from the ontology):
+
+- **Feature** — a standalone pattern a user interacts with (`List`, `Grid`, `Form`).
+- **Capability** — a composable blueprint that adds state/behavior onto a host
+  feature (`Async`, `Paginated`, `Selectable`).
+
+## Illustration
+
+This app's rendered, interactive presentation of a single blueprint. `blueprints`
+is a gallery of illustrations. "Illustration" is the noun for the whole per-blueprint
+screen; do not use "demo" (implies a live working widget — these are static) or
+"page" (routing concept, not domain).
+
+## Viewer
+
+The one reusable component that renders any blueprint's illustration. It draws the
+generic parts from a blueprint's typed data and slots in that blueprint's bespoke
+Specimen. Every illustration is the Viewer applied to one blueprint.
+
+## Specimen
+
+The interactive-looking but **static** visual mock of the blueprint's actual UI —
+the left pane of the Viewer. Bespoke per blueprint (a Grid specimen looks nothing
+like a List's). Selecting a Function highlights the region of the specimen that
+function owns. Not "mockup", not "demo".
+
+## Readout
+
+The right pane of the Viewer: the blueprint's formal contract for the selected
+Function — source capability, responsibility, state touched, behaviors (pre →
+effect), invariants, failure modes, critical-performance thresholds.
+
+## Companion
+
+A supporting schematic shown below the Viewer's two panes. Two kinds exist so far:
+the **composition map** (how a feature extends/composes with capabilities) and the
+**state machine** (the blueprint's lifecycle). A blueprint may have neither, one, or
+both.
+
+## Function
+
+One row of a blueprint's "Functional analysis" — a named responsibility of the
+pattern (e.g. List's `Display`, `Scroll`, `Load`). Functions are the unit the Viewer
+lets you explore, tab by tab. Distinct from **Behavior** (a concrete state
+transition like `loadMore()`); behaviors are the mechanics underneath a function.
+
+## Gallery
+
+The app's index (landing screen): every blueprint in the ontology, each as a card
+linking to its illustration — including blueprints not yet illustrated, shown as
+**planned**.