feat(upload): use ant-core estimate_upload_cost for pre-upload quotes

[Nic-dorman]

Summary

• Both the Estimate Cost button and the Upload dialog pre-quote used to call start_upload → file_prepare_upload, which encrypts the whole file to disk and parks a PreparedUpload for 30 minutes. Every cancelled estimate leaked hundreds of encrypted chunks into memory.
• Switch both to the new lightweight Client::estimate_upload_cost (ant-core PR fix(wallet): direct-key + Arbitrum One mainnet payments #44, merge b0c501a): samples a single network quote for a representative chunk and extrapolates. No encryption-to-spill, no parked upload, no wallet required.
• Multi-file estimates now run in parallel (Promise.all), so dialog-open latency tracks the slowest single quote instead of the sum.
• Confirm click still runs the real start_upload via startRealUpload, so the heavy work happens only on commit. Dropped the preQuote handoff plumbing and the pendingQuotes map.
• Renamed the 'quoting' status label to "Preparing upload…" now that the heavy phase sits post-Confirm.
• Removed utils/payment.ts::estimatePaymentGasCost — PR fix(wallet): direct-key + Arbitrum One mainnet payments #44's gas heuristic replaces it. Its leftover GAS_* constants and getGasPrice import go with it.

Dependency bump

ant-core pin f88c95d → b0c501a (PR #44 merge). Cascades to ant-node 0.10.0 → 0.10.1 and saorsa-core 0.23.0 → 0.23.1 via the resolver.

Test plan

• cargo check clean
• vitest — 19/19 pass
• Dev app smoke test on live network before tomorrow's release:
  • Estimate Cost (top-bar) on 3 files shows a cost within ~5 s and leaves pending_uploads empty
  • Open Upload dialog → see "Estimating cost…" → cost appears → Cancel → pending_uploads empty
  • Open Upload dialog → Confirm → "Preparing upload…" visible → upload lands on network
  • Indelible path: estimate is skipped (Indelible is server-driven cost) — verify nothing regressed
  • Tiny file (<3 bytes) rejection surfaces with a sensible error, not a crash

Known follow-ups

• If public-uploads (Visibility arg) merges upstream, estimate_file_cost needs a visibility hint so the chunk count includes the DataMap chunk for public uploads.
• CostEstimationInconclusive error path currently reaches the frontend as a generic warn + null return. A friendlier toast ("Cost estimate unavailable, try another file") would be nicer.

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