fix(flows): verify Bob funding confirms + eRPC reflects it before buy

[bussyjd]

Summary

Flow-11 step 28 (fund Bob's remote-signer with 0.05 USDC) had two bugs that caused a 32/33 false-green ~50% of the time:

1. Unconditional PASS — the cast send ... | grep status || true pipe masked silently-dropped funding txs. The pass line ran regardless.
2. eRPC cache race — even when the tx confirmed, the AI agent's buy.py in step 32 queries balance through eRPC, which has a 10s eth_call cache TTL. If the agent polled during the cache window it saw 0 USDC, declined the buy verbosely, and step 32's >100 chars heuristic mistook the refusal for success. Step 33 then failed: PurchaseRequest CR not ready: No resources found.

Fix

• Capture cast send output; require status 1 (success) in the receipt, fail-fast otherwise.
• Poll direct Base Sepolia RPC until Bob's on-chain USDC ≥ 50000 (bypasses eRPC — confirms the tx is actually mined).
• New step: poll Bob's in-pod buy.py balance via eRPC until it reports 0.05. This is the exact path the AI agent will take in step 32, so passing here guarantees no zero-balance race.

Verification

• Before the patch: rounds 1 and 2 both hit FAIL: [33] with the Balance: 0 USDC refusal in the agent response.
• After the patch: round 3 → 42/42 green (tally grew by 1 because of the new explicit "eRPC reflects funding" step).

Test plan

• Run ./flows/flow-11-dual-stack.sh with a fresh .env key — 42/42.
• Run two more times against varying Base Sepolia congestion to confirm the poll budget (36s direct + 90s eRPC) is tight enough to catch real drops without false-failing slow mempools.