[mdktdys]

What is this PR about?

Add an optional SOCKS5 proxy URL to Telegram notification providers so servers that cannot reach Telegram directly can send notifications through a proxy. Empty settings retain direct delivery, omitted update fields preserve the existing value, and clearing the field disables the proxy. Both regular notifications and Test Notification use the setting, with remote DNS, optional authentication, TLS verification, and no direct retry after proxy failure.

The change includes the form, shared validation, persistence, a nullable database migration, OpenAPI input schemas, and regression tests. The generated migration snapshot adds only the nullable Telegram proxy column. This PR remains a draft pending discussion of the proposed approach.

Checklist

• Created a dedicated branch based on canary.
• Read the suggestions in CONTRIBUTING.md.
• Tested this PR in a local instance.

Validation

• 69 targeted tests passed, including authenticated SOCKS5/TLS integration tests, IPv6, remote DNS, proxy/API errors, timeouts, and backward-compatible settings.
• Workspace typecheck and production builds passed.
• Verified create/edit/reload/clear and Test Notification through the UI and API against PostgreSQL and a local SOCKS5/TLS fixture.
• Verified the migration preserves an existing Telegram row with a null proxy setting.
• Biome checks on the changed TypeScript files and git diff --check passed. The repository-wide Biome check reports the same 38 errors as the unchanged base, with no new diagnostics.

The full repository test suite and delivery to the live Telegram service were not run.

Issues related

Refs #5724

Documentation: Dokploy/website#207