Rewrite XML watcher in Rust

[Copilot]

Replaces the bash/inotifywait implementation with a Rust binary for improved performance, reliability, and maintainability.

Core Changes

• File watching: notify crate with async I/O (tokio) replaces inotifywait
• HTTP client: reqwest with structured JSON payloads via serde
• Logging: env_logger with RUST_LOG environment variable control
• Error handling: Propagated errors with detailed logging instead of silent failures

Configuration Changes

• Removed INCLUDE_FILENAME environment variable (filename always included in payload)
• Added RUST_LOG for log level control (trace/debug/info/warn/error)

Build System

• Updated flake.nix to build Rust binary with rust-overlay and rustPlatform.buildRustPackage
• Docker image now contains single static binary instead of bash + coreutils + inotify-tools + curl + jq

Implementation Details

#[derive(Debug, Clone)]
struct Config {
    watch_dir: PathBuf,
    webhook_url: String,
    webhook_method: String,
    include_content: bool,
}

Event handling uses notify::EventKind::Create only (not Modify) to prevent duplicate webhook triggers on file write completion.

Webhook dispatch is fully async with 500ms delay to ensure files are fully written before reading.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Rewrite in rust</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Rewrite in rust #1

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