Refresh the truapi-dev-host demo branch to the 0.9 wire pairing

The demo branch behind #77 (feat/use-truapi-dev-host) still pairs @parity/truapi 0.7 (via @parity/product-sdk 0.21) with the packaged launcher, while the package itself moved to the 0.9 wire (host-rust-core#502, current product-sdk-host 0.16) after dim2 required latest — see paritytech/dim2-spa#137 for the completed migration to crib from.

What the refresh needs:

• Reinstall the file: package copy (yarn caches it; yarn install --force after rebuilding dist in the sibling checkout) so the branch gets the 0.9-pinned build.
• Bump the app's SDK to whatever product-sdk release rides sdk-host 0.16, and migrate any RFC-0022 selector spellings: {tag: "Left"|"Right"} → {tag: "Index"|"Raw"}, and the ring-VRF calls (getAccountAlias, createAccountProof) now require keyHandle (the member-key ProductAccountId). dim2's commit "feat(deps): bump product-sdk-host to 0.16" shows every site type-check finds.
• Re-run the card tour from the branch README (yarn dev:host, then get-user-id / wallet-sign-message / chain cards).

Two demo-era caveats dissolved upstream on host-rust-core main (2026-08-25) and can come off the branch docs at the same time: Previewnet signer provisioning works from a current-main CLI (JWT handshake landed; the local preview-identity-auth branch is retired, its PR closed as superseded), and the .test dotNS TLD is accepted.

Full running status: docs/truapi-dev-host-plan.md on the feat/local-cli-host branch.

Start with the feat/use-truapi-dev-host branch README and compare its SDK usage with paritytech/dim2-spa#137; rebuild dist in the sibling checkout, then force-reinstall the file package with yarn install --force. Migrate the selector spellings and ring-VRF calls, run yarn dev:host through the get-user-id, wallet-sign-message, and chain cards, and update the caveats in docs/truapi-dev-host-plan.md or branch docs.