feat: support Solana→EVM intent issuing

[Asem-Abdelhady]

What

Adds support for Solana→EVM intent issuing: a user with a Solana wallet can lock SPL tokens on Solana devnet and specify an EVM address to receive the output on any supported EVM chain.

This PR stacks on top of #37 (EVM→Solana), which must merge first.

Changes

New: solanaEscrowLib.ts

• openSolanaEscrow() calls input_settler_escrow.open() on Solana via the Anchor program
• Derives PDAs (polymer, input_settler_escrow, order_context) from config constants
• Computes orderId = keccak256(borsh(StandardOrder)) to match the Rust derive_id() logic
• Wraps the 60 s confirmation wait in Promise.race with a descriptive timeout error
• Borsh encode call wrapped in try/catch so IDL mismatches surface with context

Updated: intentFactory.ts

• New isSolanaChain(inputChain) branch in openIntent() calls openSolanaEscrow and saves the order with the Solana input settler address
• outputRecipient defaults to account() (connected EVM wallet) if not provided

Updated: IssueIntent.svelte

• EVM recipient input field appears when the input chain is Solana and the output is EVM
• Tri-state submit guard: blocks on missing Solana wallet, invalid EVM recipient, or insufficient balance

Tests

• 4 unit tests for openSolanaEscrow: empty inputs guard, happy path, Borsh encode error, and 60 s timeout

Out of scope

Proof relay and claim for Solana→EVM intents are not implemented in this PR. Once the escrow is opened on Solana, the ReceiveMessage screen renders disabled buttons with a TODO comment. The validate/claim step (relaying through the Polymer oracle to the EVM input settler) is tracked separately.

Test plan

• Connect a Solana wallet (Phantom / Solflare) on devnet
• Select a Solana input token (SOL or USDC) and an EVM output token on a supported testnet
• Confirm the EVM Recipient field appears and validates the address
• Submit — verify the Solana transaction lands on devnet explorer and the order appears in IntentList
• Confirm the Fill screen shows a disabled Fill button for EVM→Solana output rows (covered by feat: EVM → Solana intent issuing #37)
• Run bun run test:unit — 32 pass, 0 fail

Closes: V2-112

Expected output

Screen.Recording.2026-04-06.at.6.44.18.AM.mov