refactor: introduce cargo workspace + psysonic-core crate (M1/7)

First milestone of the workspace crate split. Sets up the workspace
skeleton and extracts shared logging + cross-crate port traits into a
new psysonic-core crate.

  src-tauri/Cargo.toml            now defines [workspace]; top package
                                  becomes the workspace root.
  crates/psysonic-core/           new lib crate, no Tauri-handler code:
    src/logging.rs                full logging facade (was src/logging.rs)
    src/ports.rs                  PlaybackQuery + AnalysisOrchestrator
                                  trait declarations (no impls yet)

The top crate re-exports `psysonic_core::logging` and the
`app_eprintln!` / `app_deprintln!` macros so every existing
`crate::logging::*` and `crate::app_eprintln!` callsite keeps working
unchanged.

Port traits intentionally take `tauri::AppHandle` — psysonic-core is a
workspace-internal crate, so depending on Tauri here is a feature, not
a leak. Implementers will register themselves as
`Arc<dyn PlaybackQuery>` / `Arc<dyn AnalysisOrchestrator>` Tauri State
in M2/M3.

Behaviour preserving. Cargo check + clippy --workspace clean.

src-tauri/crates/psysonic-core/src/ports.rs

@@ -0,0 +1,49 @@
+//! Cross-crate port traits.
+//!
+//! These traits exist purely to break dependency cycles that would otherwise
+//! force `psysonic-audio` ↔ `psysonic-analysis` to depend on each other in
+//! both directions. Implementers register themselves as Tauri State on app
+//! bootstrap; consumers look them up via `app.try_state::<Arc<dyn _>>()`.
+//!
+//! Layout:
+//! - `AnalysisOrchestrator`  — implemented in `psysonic-analysis`, called from
+//!   `psysonic-audio` to enqueue full-buffer loudness/waveform analysis.
+//! - `PlaybackQuery`         — implemented in `psysonic-audio` on `AudioEngine`,
+//!   called from `psysonic-analysis` to ask "is this track currently playing?".
+
+use std::future::Future;
+use std::pin::Pin;
+
+use tauri::AppHandle;
+
+/// Read-only queries about the live playback session. Implemented on
+/// `AudioEngine` in `psysonic-audio`.
+///
+/// Registered as `Arc<dyn PlaybackQuery>` in Tauri State so non-audio crates
+/// can query without taking a hard dep on the audio crate.
+pub trait PlaybackQuery: Send + Sync + 'static {
+    /// `true` if `track_id` is the track currently being decoded/played.
+    fn is_track_currently_playing(&self, track_id: &str) -> bool;
+}
+
+/// Triggers full-buffer analysis on already-captured track bytes. Implemented
+/// on `AnalysisRuntime` in `psysonic-analysis`.
+///
+/// Registered as `Arc<dyn AnalysisOrchestrator>` in Tauri State so audio
+/// callsites (`stream::ranged_http`, `stream::track_stream`, `helpers`,
+/// `play_input`, `preload_commands`) can submit without depending on
+/// `psysonic-analysis`.
+pub trait AnalysisOrchestrator: Send + Sync + 'static {
+    /// Enqueue a CPU-seed analysis pass for `track_id` over the given byte
+    /// buffer. `high_priority` mirrors the HTTP-backfill head-insertion
+    /// behaviour for the currently playing track.
+    ///
+    /// Errors are stringified — audio callers only care about pass/fail.
+    fn submit_cpu_seed<'a>(
+        &'a self,
+        app: AppHandle,
+        track_id: String,
+        bytes: Vec<u8>,
+        high_priority: bool,
+    ) -> Pin<Box<dyn Future<Output = Result<(), String>> + Send + 'a>>;
+}