docs: flip README links to docs.picpeak.app + delete docs/_to-migrate (#1000 phase 3) (#1023)

Phase 3 (final) of #1000. The deep content now lives on the docs site (PicPeak/docs#7), making docs.picpeak.app the single source of truth and removing the in-repo copies.

README links flip to docs.picpeak.app; the roadmap table is retired in favour of GitHub Issues. Deletes docs/_to-migrate/ and the five migrated pages. docs/migration-to-org.md stays — it's repo-transitional, not docs-site content.

In-app references to the deleted files are repointed at the docs site, including the CRM disclaimer strings in en.json/de.json and the contract-editor fallback.

Closes #1000.

frontend/src/i18n/locales/de.json

@@ -5830,7 +5830,7 @@
       "create": "Entwurf erstellen",
       "createdToast": "Vertrag erstellt.",
       "customer": "Kunde",
-      "disclaimerBody": "Die vorausgefüllten Baustein-Texte sind NUR BEISPIELE — vom Maintainer verfasst, nicht von einem Anwalt. Lassen Sie jeden verwendeten Baustein von Ihrem eigenen Anwalt prüfen, bevor Sie den Vertrag versenden. Siehe docs/crm-disclaimers.md.",
+      "disclaimerBody": "Die vorausgefüllten Baustein-Texte sind NUR BEISPIELE — vom Maintainer verfasst, nicht von einem Anwalt. Lassen Sie jeden verwendeten Baustein von Ihrem eigenen Anwalt prüfen, bevor Sie den Vertrag versenden. Siehe https://docs.picpeak.app/features/crm/disclaimers.",
       "disclaimerTitle": "Anwaltliche Prüfung erforderlich",
       "eventDate": "Anlassdatum",
       "eventHelp": "Wird auf den Vertrag übernommen und an jeden daraus erzeugten Anlass / jede Rechnung weitergegeben. Setzen Sie dies, damit Kundenportal und Mahn-E-Mails die richtige Bezeichnung \"Hochzeit Doe / Müller\" anzeigen.",

frontend/src/i18n/locales/en.json

@@ -5828,7 +5828,7 @@
       "create": "Create draft",
       "createdToast": "Contract created.",
       "customer": "Customer",
-      "disclaimerBody": "The seeded block bodies are EXAMPLES ONLY — written by the maintainer, not by a lawyer. Have your own lawyer review every block you include before sending the contract. See docs/crm-disclaimers.md.",
+      "disclaimerBody": "The seeded block bodies are EXAMPLES ONLY — written by the maintainer, not by a lawyer. Have your own lawyer review every block you include before sending the contract. See https://docs.picpeak.app/features/crm/disclaimers.",
       "disclaimerTitle": "Lawyer review required",
       "eventDate": "Event date",
       "eventHelp": "Snapshotted onto the contract and propagated to any event / invoice generated from it. Set this so the customer portal and dunning emails show the right \"Wedding Doe / Müller\" label.",