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.lock

@@ -1660,8 +1660,7 @@ checksum = "7edddbd0b52d732b21ad9a5fab5c704c14cd949e5e9a1ec5929a24fded1b904c"
 [[package]]
 name = "pop-telemetry"
 version = "0.12.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "36586f435a76531d01477ce20b10f18d79ffde9ec1bbb7ff0c91640476b11877"
+source = "git+https://github.com/jasonwitty/pop-cli?branch=main#16877871008c5c1167fa8d8cb9823a8d15228169"
 dependencies = [
  "dirs",
  "env_logger",