Switch to forked pop-telemetry with custom Umami endpoint support

- Use forked pop-telemetry from github.com/jasonwitty/pop-cli
- Implement init_with_website_id to configure custom endpoint and website ID
- Add --umami-endpoint and --umami-website-id CLI parameters
- Default endpoint: http://unami.wittyoneoff.com/api/send
- Default website ID: caefa16f-86af-4835-8b82-c8649aea0e2a
- Maintains backward compatibility with config file opt-out support

This allows webterm to send analytics to our self-hosted Umami instance
instead of the default pop-cli telemetry endpoint.

Cargo.toml

@@ -29,7 +29,7 @@ bytes = "1.9"
 log = "0.4"
 env_logger = "0.11"
 libc = "0.2"
-pop-telemetry = "0.12.1"
+pop-telemetry = { git = "https://github.com/jasonwitty/pop-cli", branch = "main" }
 dirs = "5.0"
 
 [lib]