Add Supplier Invoice Inquiry agent skill example - #28

What this PR adds or changes

Adds examples/supplier-invoice-inquiry-agent-skill: a markdown agent skill for Workday Financials that teaches an agent to check supplier invoice status, explain payment hold conditions and 2-way / 3-way match exceptions, and prepare AP escalation notes for Accounts Payable specialists.

It addresses an important white space in the repository: expanding community agent skills beyond HCM into Workday Financials, while enforcing strict financial compliance guardrails (masking and non-disclosure of supplier bank routing numbers, account numbers, and tax identifiers).

Checklist for new or changed examples

• The example lives entirely in its own folder under examples/
• node scripts/validate-examples.mjs --check passes (valid example.json, README present, index table in sync)
• The README says what the artifact is, how to use it, and what to change before deploying it (the "Before you deploy" section)
• No credentials, tenant names, or real personal data anywhere in the folder
• node scripts/audit-examples.mjs --dirs examples/supplier-invoice-inquiry-agent-skill passes with zero findings