TRON Phase 2: transaction preparation (preview-only)

[szhygulin]

Summary

• Adds three TRON prepare_* tools: prepare_tron_native_send, prepare_tron_token_send, prepare_tron_claim_rewards. Each calls TronGrid (createtransaction / triggersmartcontract / withdrawbalance) with visible: true, validates base58 addresses and amounts, and issues an opaque handle.
• Keeps TRON tx shape (UnsignedTronTx) and its handle store separate from EVM so send_transaction's EVM-only security pipeline (eth_call re-simulation, chain-id check, spender allowlist) can't be silently shortcut by type confusion. TRON handles are preview-only in this release; send_transaction refuses them until Phase 3 lands USB HID signing via @ledgerhq/hw-app-trx.
• TRC-20 preparation is restricted to the canonical set (USDT/USDC/USDD/TUSD) whose decimals live in the hardcoded table — unknown TRC-20s are rejected with an explicit error rather than rendered as UNKNOWN in the preview.
• Hand-rolled base58check decoder + TRC-20 ABI param encoder (no new deps; base58 alphabet + double-sha256 checksum verify in ~30 LOC).

Test plan

• npx vitest run — 285/285 pass (17 new tests in test/tron-phase2-prepare.test.ts covering base58 decode, TRC-20 param layout, POST body shape, handle issuance, and both TronGrid error shapes).
• npm run build — clean tsc.
• Manual: build-and-link the MCP, call each prepare_tron_* against a real address and cross-reference txID with a direct TronGrid call.
• Manual: confirm send_transaction refuses a TRON handle (EVM-only consume path).
• Manual: hit the 24h-cooldown branch on prepare_tron_claim_rewards and confirm TronGrid's message is surfaced verbatim.

Follow-ups

• Phase 2b: freezeBalanceV2, unfreezeBalanceV2, withdrawExpireUnfreeze for Stake 2.0 bandwidth/energy management.
• Phase 3: USB HID signing via @ledgerhq/hw-app-trx (Ledger Live's WalletConnect relay does not honor tron: — verified 2026-04-14).

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