fix: reject device signers for Solana wallets with contact sales message

[albertoelias-crossmint]

Description

Fixes WAL-9474. Device signers (P256-based) are not currently supported for Solana wallets. Previously, attempting to register one would hit the server and return a 500. This PR adds client-side guards that reject device signers early with a clear InvalidSignerError including a contact sales link.

Two entry points are guarded:

• Wallet.addSigner — rejects device signers when this.chain === "solana"
• WalletFactory.registerSigners — rejects device signers when chain === "solana" during wallet creation

Items for reviewer:

• wallet.ts uses this.chain === "solana" for the check. The class has a isSolanaWallet() helper — verify whether that should be used instead for consistency.
• Confirm InvalidSignerError is already in scope in wallet.ts (no import was added in the diff).
• No unit tests were added for the new error paths.

Test plan

• Lint passes (pnpm lint)
• Existing vitest suite passes (pnpm test:vitest)
• Manually verified error message matches the "contact sales" pattern used elsewhere in the codebase

Package updates

• @crossmint/wallets-sdk: patch (changeset added via .changeset/solana-device-signer-error.md)

Link to Devin session: https://crossmint.devinenterprise.com/sessions/1c1845672cb94db9a8f27f85b77226d0
Requested by: @albertoelias-crossmint

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[devin-ai-integration]

Original prompt from Alberto Elias

'Registering Solana device signer returns 500 on iOS' (WAL-9474)

User instruction: @devin we dont expect to support device signer in solana right now in either crossbit-main or in crossmint-sdk wallets-v1 branch. it shouldnt be a 500, we should throw the appropriate error which should include a contact sales message like we do elsewhere

[devin-ai-integration]

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[changeset-bot]

🦋 Changeset detected

Latest commit: f7ccb3d

The changes in this PR will be included in the next version bump.

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[greptile-apps]

_{Last reviewed commit: "chore: add changeset..."}

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

[github-actions]

🔥 Smoke Test Results

✅ Status: Passed

Statistics

• Total Tests: 5
• Passed: 5 ✅
• Failed: 0
• Skipped: 0
• Duration: 3.54 min

✅ All smoke tests passed!

All critical flows are working correctly.

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This is a non-blocking smoke test. Full regression tests run separately.