refactor: replace all println/eprintln with tracing

[markovejnovic]

Summary

• Add custom CliLayer tracing subscriber that routes user::stdout/user::stderr targets to the correct output streams with no tracing metadata decoration
• Replace all 93 println!/eprintln!/print!/eprint! occurrences across hm and hm-plugin-cloud crates with tracing::info!(target: "user::*", ...) calls
• Subscriber always initializes with CliLayer (user-facing output) + optional fmt layer (diagnostic tracing, --verbose only)
• Consolidate tracing/tracing-subscriber as workspace dependencies
• Upgrade clippy::print_stdout and clippy::print_stderr lints from warn to deny

Architecture

Two-layer subscriber:

1. CliLayer (always active) — filters events with target user::stdout → stdout, user::stderr → stderr, no decoration
2. FmtLayer (--verbose only) — standard tracing-subscriber fmt for diagnostics

Edge case: clap help/version/error text uses raw std::io::Write with scoped #[allow] (2 occurrences in hm-plugin-cloud/src/cli.rs).

Test Plan

• All 76 workspace tests pass
• cargo clippy --workspace clean — zero print lint violations
• CliLayer unit tests: stdout routing, stderr routing, target filtering, format args, empty messages
• Pre-existing cmd_run_local_autoselect failures confirmed unrelated (missing Python harmont module)
• Manual: hm --version prints to stdout
• Manual: hm --verbose --version shows diagnostic output on stderr
• Manual: hm run error output appears on stderr with styling