Upgrade to Rust 1.91 and migrate to pop-telemetry 0.12.1

- Updated Rust toolchain from 1.90 to 1.91 (required by pop-telemetry)
- Migrated analytics to use pop-telemetry crate for privacy-focused telemetry
- Added dirs dependency for cross-platform config directory handling
- Refactored init-config.sh to handle permission restrictions in K8s
  - Gracefully handles chown failures in restricted security contexts
  - Uses alternative copy methods (cat > file) when cp fails
  - Continues operation with warnings instead of failing
- Updated Dockerfile to use rust:1.91-slim-bookworm base image
- Changed telemetry configuration from endpoint/website_id to config file path

This addresses permission denied errors when deploying to K3s with
security contexts that prevent ownership changes on pre-existing directories.

Cargo.toml

@@ -6,7 +6,7 @@ documentation = "https://docs.rs/webterm"
 readme = "README.md"
 categories = ["web-programming", "web-programming::websocket", "web-programming::http-server", "command-line-utilities"]
 keywords = ["terminal", "xterm", "websocket", "terminus", "console"]
-version = "0.3.2"
+version = "0.3.4"
 authors = ["fabian.freyer@physik.tu-berlin.de","jasonpwitty+socktop@proton.me"]
 edition = "2021"
 license = "BSD-3-Clause"