feat(discovery): v0.33.0 — per-component snapshots + /create preset page

One substantial "discovery + completion" wave. Three sub-shots, one tag.

1. Per-component snapshot pipeline.
   - examples/showcase/src/bin/snapshot.rs gains a `--previews` mode that
     iterates every registry item, drives PreviewHost via
     ui.set_preview_name(name), and writes
     docs/img/snapshots/preview-<name>.png for each (64 PNGs at 900x600).
   - Pure SoftwareRenderer — same proven path as the section snapshots, no
     WASM flakiness. New `make snapshot-previews` target.

2. /create preset page (web/create.html).
   - Pure HTML/CSS/JS, no build step. Fetches the live registry.json from
     the deploy, groups items by category, lets the user pick a base color
     + toggle components, and live-builds the exact `npx slintcn init &&
     npx slintcn add ...` command with copy + clear actions.
   - Sticky right pane on desktop, stacked on mobile.
   - Topnav `Create` link added to landing + docs.

3. Gallery + README hero refresh.
   - Landing .gallery rotates 6 fresh captures (DataTable / Command /
     Calendar / Sidebar / Dashboard / Hotbar).
   - README hero trio swapped to DataTable / Command / Calendar so the
     README reads as 2026, not v0.13.

Closes the Tooling-track parity gap (MCP + Directory + /create all shipped).
Bump 0.32.0 -> 0.33.0; `make verify` 62/62 still green.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: stevekwon211

Makefile

@@ -1,4 +1,4 @@
-.PHONY: verify test build clippy clean snapshot
+.PHONY: verify test build clippy clean snapshot snapshot-previews
 
 # Single command for local pre-commit hygiene.
 verify: test build clippy
@@ -17,6 +17,10 @@ clippy:
 snapshot:
 	cd examples/showcase && cargo run --quiet --features snapshot --bin snapshot
 
+# Per-component PNGs via PreviewHost — one per registry item (UI + block).
+snapshot-previews:
+	cd examples/showcase && cargo run --quiet --features snapshot --bin snapshot -- --previews
+
 clean:
 	cd examples/showcase && cargo clean
 	rm -rf examples/showcase/ui/slintcn