feat: network endpoints overridable from remote config

[n13]

Summary

Remote config so far only carried feature flags. This lets it also override the URLs that bind the wallet to a network, so the mobile wallet can be moved (e.g. Planck → mainnet) without an app release. Companion server PR: Quantus-Network/quersi#3.

The wallet payload gains an optional endpoints block:

"endpoints": {
  "rpc": ["https://a1-planck.quantus.cat", "https://a2-planck.quantus.cat", "https://matcha-latte.quantus.com"],
  "graphQl": ["https://sub2.quantus.com/v1/graphql"],
  "explorer": "https://explorer.quantus.com",
  "senoti": "https://snt.quantus.com/api"
}

Absent keys keep the AppConstants defaults. A malformed block (empty list, non-URL, wrong scheme) throws a FormatException, so the whole payload is rejected and the last good config stays in effect.

What changes at runtime

• NetworkEndpoints (quantus_sdk model): the four network-bound URLs, defaults from AppConstants, validated fromJson, value equality.
• NetworkEndpointsService (quantus_sdk): holds the endpoints in effect. apply() pushes the RPC and GraphQL lists into RpcEndpointService / GraphQlEndpointService (new setEndpoints, keeps measured latency for URLs that stay) and clears SubstrateService chain caches, since genesis hash and runtime version belong to one chain.
• RemoteConfigNotifier applies the cached endpoints in its constructor (before any widget can hit the network) and again when a remote sync changes them.
• SenotiService and the three explorer-link builders read from NetworkEndpointsService().current instead of AppConstants.
• RemoteConfigModel drops the match/compare boilerplate for value equality via DeepCollectionEquality, so remote != state in the notifier is a real comparison and the cache is only rewritten on change.

Bundled polkadart metadata is intentionally untouched: the runtime about to land on Planck is the same one mainnet ships, so only the endpoints differ.

When quersi is unreachable

Remote config never blocks or breaks the wallet:

• Startup applies the cached config synchronously (last successful fetch; the in-code AppConstants defaults on first run or when the cache is unreadable). The remote fetch runs unawaited in the background.
• Every quersi request is bounded to 10s, so a black-holed host cannot stall the sync or wedge the refresh guard.
• Any failure (DNS, timeout, non-200, bad JSON, malformed endpoints) is logged and yields no remote config; the current flags and endpoints stay in effect. Nothing is surfaced to the user.
• Covered by mobile-app/test/unit/remote_config_service_test.dart: an unreachable server leaves RemoteConfigModel.defaults and the built-in RPC endpoints in place; a reachable one applies its flags and endpoints.

Hard-coded URL inventory

Network-bound, now overridable: rpcEndpoints, graphQlEndpoints, explorerEndpoint, senotiEndpoint.

Left as constants on purpose:

• quersiEndpoint: the bootstrap URL that fetches the config itself.
• telemetryUrl (telemetry.quantus.cat): network-bound but only opened as a web link from the mining screen. Easy to add to the block later if wanted.
• Marketing/support links (websiteBaseUrl, techSupportUrl, termsOfServiceUrl, quest pages, communityUrl, faucetUrl, miningSetupGuideUrl, shareUrl, Keystone store URL).
• Swap externals (1click.chaindefuser.com tokens, CoinGecko prices and icons), Supabase URL from .env.
• miner-app MinerConfig.availableChains (dev/dirac/planck RPC + subsquid): the miner has its own chain picker and does not use remote config.
• Dev tooling: polkadart codegen wss://a1-planck.quantus.cat in quantus_sdk/pubspec.yaml, scripts/debug_subsquid.sh, test_qr_payload.sh.

Test plan

• flutter analyze --fatal-infos clean on quantus_sdk, mobile-app, cold-wallet-app, miner-app.
• flutter test --exclude-tags=native in quantus_sdk: 481 passed (new: network_endpoints_test, remote_config_model_test, network_endpoints_service_test).
• flutter test in mobile-app: 424 passed.
• Manual: serve a config with a different endpoints.rpc and confirm the log line Switching network endpoints to … and that subsequent RPC calls hit the new host.