add dolibarr-payments-state skill for cash receipt tracking

V2 in the dolibarr-* family. Three workflows:

- km-payment-state.sh: per-invoice reconciliation (TTC vs sum of
  payments) with OK / PARTIAL / UNPAID / OVERPAID classification.
  More honest than the `paye` boolean for deferred-cycle agreements.
- km-payment-timeline.sh: all KM payments sorted by date with
  cumulative balance — the foundation for cohort-review deferred
  9-month-cycle tracking (actual cash receipts vs contractual schedule).
- payments-by-month.sh: monthly aggregation, KM-scoped by default
  or --all-clients for accounting basis.

Also updates dolibarr/SKILL.md endpoint catalogue with
/invoices/{id}/payments (note the date-as-string vs unix-epoch quirk)
and /bankaccounts, plus captures the corresponding examples.

V1 baseline of live data: KM is fully reconciled across 5 invoices
(1 avoir + 4 regular), 8160 € total cash receipts spread Feb/Mar/Apr 2026,
all on WISE EURO (BE).

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

.claude/skills/dolibarr/examples/invoices_12_payments.json

@@ -0,0 +1,12 @@
+[
+    {
+        "amount": "5100.00000000",
+        "type": "VIR",
+        "typeline": "payment",
+        "date": "2026-03-12 12:00:00",
+        "num": "",
+        "ref": "REC003-CL00002",
+        "ref_ext": "",
+        "fk_bank_line": "19"
+    }
+]