Support first-signer case for /open/multisigOperation deep link

The pending-operation model assumed a call already exists on-chain
(Multisig.Multisigs entry with a Timepoint) before it could be
reviewed or signed. A signatory who is the first to see a brand-new
call - reachable via the deep link before anyone has submitted
anything - hit "operation not found" and the screen refused to open,
even though the deep link already carried the call's data in its
callData param (previously decoded only to format Executed/Rejected
dialog text, then discarded for the Active case that needed it).

- PendingMultisigOperation.timePoint/depositor are now nullable to
  represent "not yet submitted"; composeMultisigAsMulti's
  maybeTimePoint parameter already accepted null (used for ordinary
  first-time multisig-origin submissions via MultisigSigner), so the
  pallet-call layer needed no changes.
- New PendingMultisigOperation.notYetSubmitted(...) factory and
  MultisigOperationDetailsInteractor.buildNotYetSubmittedOperation()
  build a synthetic operation from the deep link's callData, hash
  verified against the URL's callHash rather than trusted blindly.
- OperationIsStillPendingValidation now skips its on-chain
  "still pending" check for a not-yet-submitted operation, since it
  would otherwise always fail and block the very first submission.
- MultisigOperationPayload carries the callData through so both the
  details screen and the full-details screen (independently reachable
  via "Call Details", since that button is available whenever call
  data is known) can construct the synthetic operation.

feature-account-api/src/main/java/io/novafoundation/nova/feature_account_api/data/multisig/model/PendingMultisigOperation.kt

@@ -4,6 +4,7 @@ import io.novafoundation.nova.common.address.AccountIdKey
 import io.novafoundation.nova.common.address.toHex
 import io.novafoundation.nova.common.utils.Identifiable
 import io.novafoundation.nova.feature_account_api.domain.model.MetaAccount
+import io.novafoundation.nova.feature_account_api.domain.model.MultisigMetaAccount
 import io.novafoundation.nova.feature_account_api.domain.model.addressIn
 import io.novafoundation.nova.feature_account_api.domain.multisig.CallHash
 import io.novafoundation.nova.runtime.multiNetwork.chain.model.Chain
@@ -18,9 +19,24 @@ class PendingMultisigOperation(
     val call: GenericCall.Instance?,
     val callHash: CallHash,
     val chain: Chain,
-    val timePoint: MultisigTimePoint,
+    /**
+     * Null means this call has never been submitted on-chain yet (no `Multisig.Multisigs` entry
+     * exists) - the "first signer" case reachable via a `/open/multisigOperation` deep link
+     * before anyone has signed. `composeMultisigAsMulti`'s `maybeTimePoint` parameter already
+     * accepts null for exactly this (see `MultisigSigner.wrapCallsInAsMulti`, which uses the
+     * same null-timepoint-for-first-submission pattern for ordinary multisig-origin calls) -
+     * this model just didn't have a way to represent that state before.
+     */
+    val timePoint: MultisigTimePoint?,
     val approvals: List<AccountIdKey>,
-    val depositor: AccountIdKey,
+    /**
+     * Null for the same not-yet-submitted case as [timePoint] - nobody has deposited/proposed
+     * this call yet, so there is no depositor. [userAction] already handles this correctly:
+     * comparing [signatoryAccountId] to a null depositor is simply never true, so a signatory
+     * viewing a not-yet-submitted call is never offered "Reject" (rejecting something that was
+     * never proposed makes no sense - only cancel_as_multi on an *existing* operation does).
+     */
+    val depositor: AccountIdKey?,
     val deposit: BigInteger,
     val signatoryAccountId: AccountIdKey,
     val signatoryMetaId: Long,
@@ -30,6 +46,9 @@ class PendingMultisigOperation(
 
     val operationId = PendingMultisigOperationId(multisigMetaId, chain.id, callHash.toHex())
 
+    val isSubmittedOnChain: Boolean
+        get() = timePoint != null
+
     override val identifier: String = operationId.identifier()
 
     override fun toString(): String {
@@ -78,3 +97,35 @@ fun PendingMultisigOperation.Companion.createOperationHash(metaAccount: MetaAcco
 fun PendingMultisigOperationId.Companion.create(metaAccount: MetaAccount, chain: Chain, callHash: String): PendingMultisigOperationId {
     return PendingMultisigOperationId(metaAccount.id, chain.id, callHash)
 }
+
+/**
+ * Builds a synthetic [PendingMultisigOperation] for a call that has never been submitted
+ * on-chain - the deep-link "first signer" case (see `MultisigOperationDetailsDeepLinkHandler`
+ * and `RealMultisigOperationDetailsInteractor.buildNotYetSubmittedOperation`). Unlike
+ * `PendingMultisigOperation.from` (used by the chain-storage-driven syncer), this never touches
+ * chain state - everything it needs (threshold, other signatories) is already known locally
+ * from the already-added [MultisigMetaAccount], and [call] comes from the deep link's `callData`
+ * param, whose hash the caller must already have verified matches the link's `callHash`.
+ */
+fun PendingMultisigOperation.Companion.notYetSubmitted(
+    multisigMetaAccount: MultisigMetaAccount,
+    call: GenericCall.Instance,
+    callHash: CallHash,
+    chain: Chain,
+    timestamp: Duration,
+): PendingMultisigOperation {
+    return PendingMultisigOperation(
+        multisigMetaId = multisigMetaAccount.id,
+        call = call,
+        callHash = callHash,
+        chain = chain,
+        timePoint = null,
+        approvals = emptyList(),
+        depositor = null,
+        deposit = BigInteger.ZERO,
+        signatoryAccountId = multisigMetaAccount.signatoryAccountId,
+        signatoryMetaId = multisigMetaAccount.signatoryMetaId,
+        threshold = multisigMetaAccount.threshold,
+        timestamp = timestamp,
+    )
+}

feature-account-api/src/main/java/io/novafoundation/nova/feature_account_api/view/TableCellViewExt.kt

@@ -53,7 +53,7 @@ fun TableCellView.showWallet(walletModel: WalletModel) {
     walletModel.icon?.let(::setImage)
 }
 
-fun TableCellView.showAccountWithLoading(loadingState: ExtendedLoadingState<AccountModel>) {
+fun TableCellView.showAccountWithLoading(loadingState: ExtendedLoadingState<AccountModel?>) {
     showLoadingState(loadingState) {
         showAccount(it)
     }