feat(host,signer): wrap account.signVrf in the accounts surface

[Imod7]

Closes #288
Part of #286

Description

Adds signVrf to the accounts surface so products can produce an sr25519 VRF signature
over a Merlin transcript without going through the raw truAPI client.

Changes

File	Change	Impact
packages/host/src/accounts.ts	signVrf on AccountsProvider and its adapter, plus the VrfTranscriptItem, VrfSignature and ProductAccountLookup types	New public method. Callers pass and receive Uint8Array; the adapter handles hex encoding and the tagged derivation index
packages/host/src/index.ts	Export the three new types	Types are usable by name
packages/host/src/testing.ts	Test driving the shipped fake through the real adapter	Catches a fake that stops matching what the adapter decodes. This fake is the only way a product can test a VRF flow
packages/signer/src/providers/host.ts	HostProvider.signVrf, the internal provider interface, and type re-exports from host	Same call reachable from the signer, with the signer error types
packages/signer/src/signer-manager.ts	SignerManager.signVrf	Reachable from the object most products already hold
packages/signer/src/index.ts	Export the three types	Types are usable by name
pending-changesets/accounts-sign-vrf.md	Changeset, minor for host, signer and the umbrella	Release notes and version bumps

Two earlier commits also route getProductAccount and getProductAccountSigner through
one account-reference type, so the tagged derivation index is built in a single place.

Why these changes

The hosts have implemented account.signVrf for a while, but no SDK accessor exposed it.
Products that needed it had to call getTruApi() directly and hand roll hex encoding,
account addressing and error handling. That also pins the product to the truAPI wire
format, which the SDK is supposed to absorb.

The concrete consumer is the airdrop lottery ticket on the People chain, which cannot be
produced in hosted mode today.

Breaking change

AccountsProvider is an exported interface and signVrf is a required member, so
anything that implements it, including hand written test doubles, must add the method.
Code that only calls the provider is unaffected. The fake in
@parity/product-sdk-host/testing already implements it.

Testing

cd product-sdk
pnpm install
pnpm -r build
pnpm -r --no-bail test -- --run
pnpm typecheck
pnpm check

Unit test results:

 pnpm --filter "@parity/product-sdk-host"   test -- --run
 pnpm --filter "@parity/product-sdk-signer" test -- --run

Package	Before	After
@parity/product-sdk-host	87 passed	92 passed
@parity/product-sdk-signer	107 passed	113 passed

All other packages are unchanged and green. pnpm typecheck and pnpm check are clean.

[github-actions]

📦 Bundle size impact

Comparing 2026-08-11T11:23:30.079Z → 2026-08-11T11:23:39.051Z

	Package	Entry	Bundled before	Bundled after	Δ	Ship gzip Δ	Shake ratio
🟢	@parity/product-sdk	.	6.33 MB	6.33 MB	+775 B (+0.0%)	0 B	0% (was 0%)
🟢	@parity/product-sdk	./core	6.33 MB	6.33 MB	+775 B (+0.0%)	0 B	0% (was 0%)
🟢	@parity/product-sdk	./host	84.2 KB	84.4 KB	+221 B (+0.3%)	0 B	2% (was 2%)
🟢	@parity/product-sdk	./react	6.34 MB	6.34 MB	+775 B (+0.0%)	0 B	0% (was 0%)
🟢	@parity/product-sdk	./wallet	182.0 KB	182.7 KB	+771 B (+0.4%)	0 B	1% (was 1%)
🟢	@parity/product-sdk-host	.	84.2 KB	84.4 KB	+221 B (+0.3%)	+94 B	2% (was 2%)
🟢	@parity/product-sdk-signer	.	182.0 KB	182.7 KB	+771 B (+0.4%)	+241 B	1% (was 1%)
🟢	@parity/product-sdk-statement-store	.	95.7 KB	95.9 KB	+221 B (+0.2%)	0 B	10% (was 11%)

Thresholds — warn: ≥10% or ≥5.0 KB · fail: ≥20% or ≥15.0 KB (bundled). Percentage only applies once the baseline is ≥ 10 KB.

[TarikGul]

Looks good - lets get the e2e test fixed.

[Imod7]

Looks good - lets get the e2e test fixed.

Thanks! On the e2e failures, I looked into these and I also run locally and they are not coming from this PR. I will dig more in the e2e failures and I will open a separate PR for this.