feat(v2): commission split target accepts wallet id, invoice key, LN address, or LNURL

Closes the operator-facing limitation that commission split legs could
only target the operator's own LNbits wallets. Adopting the splitpayments
pattern — a single `target` string accepts:
  - LNbits wallet id (UUID-shaped) — direct internal pay
  - LNbits wallet invoice key — resolved via get_wallet_for_key, then
    internal pay (lets the operator split to any LNbits user who shares
    their invoice key)
  - Lightning address (user@domain) — resolved via LNURL-pay
  - LNURL string (LNURL1...) — resolved via LNURL-pay

Schema (m001 update — fresh-install only; no operator data in production):
  dca_commission_splits.wallet_id → target

Backend (distribution.py):
  - New _pay_split_leg helper: routes the leg by target type. External
    targets (@ or LNURL prefix) go through get_pr_from_lnurl + pay_invoice;
    internal targets go through create_invoice + pay_invoice (the original
    path), with get_wallet_for_key as the first resolution step so
    invoice keys work as well as wallet ids.
  - _pay_operator_splits delegates per-leg payment to the new helper.
  - dca_payments rows still record the leg as leg_type='operator_split';
    external targets land destination_ln_address (the human-readable
    target), internal targets land destination_wallet_id.
  - Errors are caught and surfaced via the existing failed-leg path
    so /retry can re-run them.

Frontend (commission tab):
  - Each leg gets a per-row q-btn-toggle: "My wallet" vs "Lightning
    address / LNURL / invoice key". Wallet mode shows the q-select of
    the operator's own wallets (previous behaviour); external mode
    shows a free-text q-input.
  - On load, targetKind is inferred from whether the stored target
    matches one of the operator's wallet ids (renders as 'wallet')
    or not (renders as 'external'). The kind is UI-only, not persisted.
  - Leg row laid out in a bordered card so the toggle + 3-column layout
    don't crowd at narrow widths.

Refs: aiolabs/satmachineadmin#9

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

static/js/index.js

@@ -1080,8 +1080,12 @@ window.app = Vue.createApp({
         const {data} = await LNbits.api.request(
           'GET', `${COMMISSION_SPLITS_PATH}${params}`
         )
+        // targetKind is a UI-only hint derived from the stored target string.
+        // It's not persisted server-side; the server resolves the target
+        // at payment time regardless.
         this.commissionLegs = (data || []).map(leg => ({
-          wallet_id: leg.wallet_id,
+          target: leg.target || '',
+          targetKind: this._inferTargetKind(leg.target),
           label: leg.label || '',
           pct: Number(leg.pct) || 0
         }))
@@ -1091,9 +1095,19 @@ window.app = Vue.createApp({
       }
     },
 
+    _inferTargetKind(target) {
+      // If the value matches one of the operator's own wallet ids, render
+      // the row in 'wallet' mode (q-select). Otherwise treat as external
+      // (free-text q-input).
+      if (!target) return 'wallet'
+      const ownIds = new Set(this.walletOptions.map(w => w.value))
+      return ownIds.has(target) ? 'wallet' : 'external'
+    },
+
     addCommissionLeg() {
       this.commissionLegs.push({
-        wallet_id: this.walletOptions[0]?.value || null,
+        target: this.walletOptions[0]?.value || '',
+        targetKind: 'wallet',
         label: '',
         pct: 0
       })
@@ -1110,7 +1124,7 @@ window.app = Vue.createApp({
       const body = {
         machine_id: this.commissionScope,
         legs: this.commissionLegs.map((leg, idx) => ({
-          wallet_id: leg.wallet_id,
+          target: (leg.target || '').toString().trim(),
           label: leg.label || null,
           pct: Number(leg.pct),
           sort_order: idx