feat: SPL token display and send support

[BitHighlander]

Summary

• Fix token visibility: case-insensitive CAIP networkId matching (Pioneer returns lowercase, pioneer-caip uses mixed case) — was silently dropping all Solana SPL tokens
• Fix SendForm: isTokenSend now recognizes /token:, /spl:, /trc20: CAIP patterns (was erc20-only)
• Add SPL token transfer path in txbuilder — routes to Pioneer's new build-transfer-token endpoint
• Handle MAX send for SPL tokens using frontend-provided tokenBalance

Dependencies

• Requires Pioneer PR: https://github.com/coinmastersguild/pioneer/pull/14 (adds POST /solana/build-transfer-token)

Test plan

• Verify SPL tokens (USDC, etc.) appear under Solana chain after balance refresh
• Click SPL token → verify send form shows token symbol/balance (not SOL)
• Build SPL token transfer → verify Pioneer endpoint called with correct mint + amount
• Sign on device → broadcast → verify txid returned
• Test MAX send for SPL token
• Verify native SOL send still works (regression)
• Verify EVM token sends still work (regression)