feat(turbodocx-sdk): add the 5 new signature webhook events (7-event parity)

The July release expanded TurboSign signature webhooks from 2 → 7 events. The turbodocx-sdk quickstart skill references still enumerate only the 2 old events, so generated integration code is behind the real event set.

Current: skills/turbodocx-sdk/references/{javascript,python,go,php,java}.md list only signature.document.completed / signature.document.voided in their events: [...] subscription arrays and per-event handler switches.

Needed: add the 5 new events — signature.document.sent, .viewed, .signed, .recipient_signed, .finalization_failed — across all 5 language templates, note the recipient_signed vs signed vs completed branching, and extend evals/evals.json.

Why this ticket exists: the 2026-07-09 webhook parity batch covered every other track (Docs #91 user docs — merged; Docs #90 SDK-ref pages; SDK #38; n8n #5) but skipped the quickstart skill. Source of truth = backend WebhookEvents enum (src/models/Webhook/IWebhook.ts).

Start with src/models/Webhook/IWebhook.ts to confirm the WebhookEvents enum, then update skills/turbodocx-sdk/references/{javascript,python,go,php,java}.md and evals/evals.json. Check each events array and per-event handler switch, preserving the recipient_signed versus signed versus completed branching. Done means all five templates and the evaluations cover the seven signature events.