refactor: replace UserInput(String) with typed TaskError variants

[Copilot]

TaskError::UserInput(String) was a catch-all used in ~70 places across 25+ files — effectively Generic(String) renamed, defeating the goal of typed error granularity. This PR deletes UserInput and replaces every callsite with a purpose-specific variant.

New TaskError variants

Domain	Variants
SDK/RPC setup	SdkInitializationFailed (covers provider binding too), RpcProviderCreationFailed (covers Core RPC client creation too), InvalidCoreWalletName, NoCoreWalletsLoaded
SPV	SpvClearDataFailed, SpvStartFailed, SpvBroadcastFailed
UTXO / asset lock	UtxoUpdateFailed, AssetLockTransactionBuildFailed, WalletPaymentFailed
Wallet key/address	WalletKeyLookupFailed, WalletAddressDerivationFailed
Payment	InvalidRecipientAddress, AddressNetworkMismatch, NoUtxosAvailable, InsufficientFunds, OutputTooSmallForFee, SighashComputationFailed
Token queries	NoIdentitiesFound, NotContractOwner, NotDesignatedTokenRecipient, NotEvonode
Wallet identity loading	WalletIdentityNotFound, WalletIdentityKeyMismatch, NoMatchingWalletKeys, WalletKeyDerivationPathNotFound, NoWalletIdentitiesFound
Key validation	KeyInputValidationFailed, PublicKeyMapBuildFailed, WalletInfoDeterminationFailed
Voting / DPNS	NoVotingIdentity, NoDocumentSigningKey

New DashPayError variants

• MissingAuthenticationKey — replaces string-checked "no suitable authentication key" across profile.rs, contact_info.rs, contact_requests.rs
• ContactRequestAlreadySent { to: String } — replaces string-formatted duplicate-request check

Token distribution recipient variants

NotTokenDistributionRecipient { reason: &'static str } is replaced with three typed variants that carry structured context data:

• NotContractOwner { contract_owner: String } — includes the contract owner's base58 ID
• NotDesignatedTokenRecipient { designated_recipient: String } — includes the designated recipient's base58 ID
• NotEvonode — for evonode-only distributions

detail: String → #[source] conversions

Five variants now use a #[source]-annotated concrete error type (following the DpnsFetchError pattern) instead of a detail: String field:

• AssetLockAddressDerivationFailed { #[source] source: dashcore::address::Error }
• AddressConversionFailed { #[source] source: Box<ProtocolError> }
• InvalidRecipientAddress { address: String, #[source] source: dashcore::address::Error }
• AddressNetworkMismatch { #[source] source: dashcore::address::Error }
• SighashComputationFailed { #[source] source: dashcore::sighash::Error }

Remaining detail: String variants are kept as-is because their upstream functions return String errors.

Notable structural fix

The fragile string-prefix match in load_identity_from_wallet.rs is replaced with a proper variant match:

// Before — brittle string matching
Err(TaskError::UserInput(ref msg))
    if msg.starts_with("No identity found for wallet identity index") => continue,

// After — typed match
Err(TaskError::WalletIdentityNotFound { .. }) => continue,

DashPay callsites

DashPay functions now return proper DashPayError variants (MissingEncryptionKey, MissingDecryptionKey, ValidationFailed, InvalidQrCode, UsernameResolutionFailed, etc.) which auto-convert to TaskError via From<DashPayError>.

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[lklimek]

@copilot merge CoreRpcClientCreationFailed and RpcProviderCreationFailed into one error

[Copilot]

Done in commit 2301035. CoreRpcClientCreationFailed has been removed and its callsite in context/mod.rs now uses RpcProviderCreationFailed { detail: e.to_string() }.

[lklimek]

@copilot merge ContextProviderBindFailed into SdkInitializationFailed

[Copilot]

Done in commit 2301035. ContextProviderBindFailed has been removed. Both bind_app_context() callsites in context/mod.rs now use SdkInitializationFailed. The doc comment on SdkInitializationFailed was updated to mention it also covers provider binding failures.

[lklimek]

@copilot we don't want to include string reason here. Consider separate variants , with field for context data (allowed recipients, actual recipient, etc.)

[Copilot]

Done in commit 2301035. Replaced NotTokenDistributionRecipient { reason: &'static str } with three typed variants carrying structured context:

• NotContractOwner { contract_owner: String } — shows the owner's base58 ID
• NotDesignatedTokenRecipient { designated_recipient: String } — shows the designated recipient's base58 ID
• NotEvonode — no context needed (the message is self-explanatory)

[lklimek]

@copilot review all errors in this file that use detail as string and check if we can just replace it with the source error (rename field to source, annotate #[source], use concrete erorr type). See DpnsFetchError for an example.

[Copilot]

Done in commit 2301035. Reviewed all detail: String fields. Five converted to #[source] with concrete types (following the DpnsFetchError pattern):

• AssetLockAddressDerivationFailed → #[source] source: dashcore::address::Error
• AddressConversionFailed → #[source] source: Box<ProtocolError>
• InvalidRecipientAddress → #[source] source: dashcore::address::Error (kept address: String for the user message)
• AddressNetworkMismatch → #[source] source: dashcore::address::Error
• SighashComputationFailed → #[source] source: dashcore::sighash::Error

The remaining detail: String fields (WalletAddressProviderSetupFailed, SpvClearDataFailed, UtxoUpdateFailed, WalletKeyLookupFailed, WalletAddressDerivationFailed, SdkInitializationFailed, etc.) could not be changed because their upstream functions return String errors — there is no concrete typed error to propagate.