fix(swift-example-app): point regtest+docker SPV at dashmate seed port

[QuantumExplorer]

Issue being fixed or feature implemented

When the user enables "Use Docker Setup" on regtest, SPV silently fails to connect:

```
INFO dash_spv::network::manager: Reconnecting to exclusive peer: 127.0.0.1:19999
INFO dash_spv::network::peer: Peer 127.0.0.1:19999 closed connection (EOF)
ERROR dash_spv::network::handshake: Error receiving message during handshake: Peer disconnected
WARN dash_spv::network::manager: Handshake failed with 127.0.0.1:19999: Peer disconnected
```

`19999` is testnet's standard P2P port. dashmate's local cluster doesn't run on it — its seed lives at `127.0.0.1:20301` for the default 3-node local preset.

The bug is bleed-through between two mutually-exclusive UI surfaces that share the same `UserDefaults` keys:

• The OptionsView "Use Custom SPV Peers" toggle (shown only on non-regtest networks) seeds `localCorePeers` with the active network's standard P2P port — `127.0.0.1:19999` for testnet.
• The OptionsView "Use Docker Setup" toggle (shown only on regtest) flips `useLocalhostCore = true` but doesn't touch `localCorePeers`.
• `CoreContentView.startSync` reads both keys verbatim. The stale testnet peer string is the result.

What was done?

Replaced the inline `UserDefaults` lookup in `startSync` with a `spvPeerOverride()` helper that selects the peer list based on `(currentNetwork, useDockerSetup)`:

• regtest + docker → `["127.0.0.1:20301"]`. Ignores `localCorePeers` entirely so the stale testnet/mainnet value can't bleed in. The port comes from dashmate: base 20001 per `getLocalConfigFactory.js` + `i*100` per `setupLocalPresetTaskFactory.js` with seed at `i = nodeCount`, so the 3-node default puts `local_seed` at 20301.
• non-regtest + `useLocalhostCore` → parses `localCorePeers` as before for the existing custom-peer flow.
• otherwise → empty list; FFI uses the network's built-in seed nodes.

`startSync` derives `restrictToConfiguredPeers` from whether the override returned anything, so the call site no longer juggles two flags.

How Has This Been Tested?

• `xcodebuild -project SwiftExampleApp.xcodeproj -scheme SwiftExampleApp -sdk iphonesimulator` passes.
• Manually on the simulator pointing at a running dashmate local cluster: with the previous bleed-through state (`localCorePeers = 127.0.0.1:19999` from a prior testnet session), switching to regtest + docker and starting SPV used to spin on "Peer disconnected". After the fix the same flow connects to `127.0.0.1:20301`, completes handshake, and syncs headers cleanly. Filter sync also works once dashmate's compact-filter index is on (see feat(dashmate): default-on the BIP158 compact-filter index across all presets #3587).

Breaking Changes

None. The non-regtest custom-peers flow reads `localCorePeers` exactly as before. The regtest+docker flow now uses a hard-coded peer; users with a non-default dashmate `nodeCount` (where the seed lands at a different port) will need either a non-default-aware override or to run the typical 3-node preset. Future PR could surface a "Docker Seed Port" override field in OptionsView for that edge case — not blocking the bug fix.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 95e5ef29-7498-4920-af7f-a467e9e3467e

📥 Commits

Reviewing files that changed from the base of the PR and between 318d83b and c86e5ea.

📒 Files selected for processing (1)

• packages/swift-sdk/SwiftExampleApp/SwiftExampleApp/Core/Views/CoreContentView.swift

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/swift-example-app-regtest-spv-peer

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[thepastaclaw]

Review Gate

Commit: c86e5eaf

• ✅ Debounce: 49m ago (need 30m)

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[github-actions]

✅ DashSDKFFI.xcframework built for this PR.

• Workflow run: https://github.com/dashpay/platform/actions/runs/25376324527
• Artifacts: DashSDKFFI.xcframework (folder), DashSDKFFI.xcframework.zip, xc_checksum.txt

SwiftPM (host the zip at a stable URL, then use):

.binaryTarget(
  name: "DashSDKFFI",
  url: "https://your.cdn.example/DashSDKFFI.xcframework.zip",
  checksum: "e1f796da4fdda0a2f814f455979201f26e47f64b909cbb8e3c757d9bbfa0e78d"
)

Xcode manual integration:

• Download 'DashSDKFFI.xcframework' artifact from the run link above.
• Drag it into your app target (Frameworks, Libraries & Embedded Content) and set Embed & Sign.
• If using the Swift wrapper package, point its binaryTarget to the xcframework location or add the package and place the xcframework at the expected path.

[QuantumExplorer]

Self Reviewed