[Bug/UX] Trading Widget — Zap follow-up fixes

[realproject7]

Summary

Multiple UX improvements and HUNT/USDC zap bugs for the TradingWidget after mainnet Zap launch.

1. [Bug] HUNT and USDC zap txs revert on mainnet

Priority: High

Both HUNT and USDC mint via ZapPlotLinkV2 revert on Base mainnet. The E2E Foundry script (PR #61) passed for HUNT, but frontend txs fail. MetaMask warns "This transaction is likely to fail" before submission.

HUNT revert:

• Tx: 0x7287f26fc7309d3f11e809c3c6645c02234fa25e7ef3f9a2eebb70a0a7b9d363
• Block: 43733619
• Method: mint(HUNT, 0x25617...7c379, 10000...00000, 19356...56092)
• Value: 0 ETH

USDC revert:

• Tx: 0xf288c9d570539fe7bf9f1ed54cd2cded6dd22c23605d99ce5a6fcd5a7f496c0e
• Block: 43733866
• Method: mint(USDC, 0x25617...7c379, 10000...00000, 8414)
• Value: 0 ETH

Note: ETH zap works fine. Only ERC-20 input tokens (HUNT, USDC) revert.

Investigate root cause. Possible issues:

• HUNT/USDC approval to Zap contract insufficient or approving wrong address
• Frontend passing wrong maxFromTokenAmount (check slippage calculation)
• Contract's ERC-20 safeTransferFrom failing (allowance, balance, or Permit2 issue)
• Different execution context between Foundry script (deployer direct) and frontend (wagmi/wallet)
• USDC's 6-decimal handling causing overflow in contract

Debug by simulating the exact tx calldata via cast call --trace on both failed txs.

2. [UX] Insufficient balance warning for all token options

The "Insufficient balance" error text already exists but may not show for all zap modes. Verify it displays correctly when:

• ETH balance < estimated cost
• HUNT balance < estimated cost
• USDC balance < estimated cost
• PLOT balance < estimated cost

3. [UX] Show wallet balance below "Pay with" line

Move the balance display from below the amount input to directly below the "PAY WITH" token selector. Show the selected token's balance prominently so users see it before entering an amount.

Format: Balance: 0.0262 ETH / Balance: 100 HUNT / Balance: 0 USDC / Balance: 1816.34 PLOT

4. [UX] "Max" input button for all token options

Add a MAX button on the buy tab (currently only exists on sell tab). For buy mode, MAX should:

• For PLOT: set amount to max storyline tokens buyable with full PLOT balance (use estimateMintReverse)
• For ETH/USDC/HUNT: set amount to max storyline tokens buyable with full balance via Zap (use estimateMintReverse with exact-input mode)
• Leave a small ETH buffer for gas when using ETH (~0.001 ETH)

5. [UX] Label change: "TOKENS TO BUY" → "STORY TOKENS TO BUY"

Simple text change in the buy tab label.

6. [UX] Rename "Trade" to "Trade to Support" + tooltip

• Change section title from "Trade" to "Trade to Support" (both the collapsible header and the box <h2>)
• On the "Trade to Support" title, add a tooltip (hover/tap) explaining: "Every trade generates a 5% creator royalty — buying and selling these story tokens directly supports the writer to keep continuing this story."
• Button text: keep as "Buy with {token}" (no change needed)

Acceptance Criteria

• HUNT and USDC zap bug identified and fixed (both contract and frontend if needed)
• Insufficient balance warning shows for all 4 token options
• Balance displayed below "Pay with" selector
• MAX button works on buy tab for all token options
• Label changed to "STORY TOKENS TO BUY"
• "Trade" renamed to "Trade to Support" with tooltip
• Build passes

Branch

task/445-trading-widget-fixes in plotlink repo (+ plotlink-contracts if contract fix needed)

[realproject7]

All fixes merged. HUNT OOG fixed (5M gas), USDC contract bug fixed (redeployed to 0x04f557F8D2806B34FC832a534c08DF514D4dfEeF). UX: balance below Pay With, MAX on buy, Story tokens label, Trade to Support + tooltip. PR #446 merged.