chore: consolidate all in-progress parallel-session WIP

Wholesale commit of every uncommitted change across the tree, at the user's
explicit request — host refactor-campaign W1 (native.rs facade + native/ dir,
library/ + mgmt/ splits), Android, core. These streams were mid-flight and not
individually built/tested together; this supersedes the per-session HOLD
markers. Consolidating so everything lands on main in one pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/mgmt/session.rs

@@ -0,0 +1,65 @@
+//! Session-tagged management endpoints: stop the active session, force an IDR. Split out of the
+//! `mgmt` facade (plan §W5).
+
+use super::shared::*;
+use std::sync::atomic::Ordering;
+
+/// Stop the active session
+///
+/// Kicks the connected client: stops the video/audio stream threads and clears the launch
+/// state. Idempotent — succeeds even when nothing is streaming.
+#[utoipa::path(
+    delete,
+    path = "/session",
+    tag = "session",
+    operation_id = "stopSession",
+    responses(
+        (status = NO_CONTENT, description = "Session stopped (or none was active)"),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+    )
+)]
+pub(crate) async fn stop_session(State(st): State<Arc<MgmtState>>) -> StatusCode {
+    let was_streaming = st.app.streaming.swap(false, Ordering::SeqCst);
+    st.app.audio_streaming.store(false, Ordering::SeqCst);
+    *st.app.launch.lock().unwrap() = None;
+    *st.app.stream.lock().unwrap() = None;
+    // Native plane: the GameStream flags above don't reach it (it runs its own loops off the shared
+    // session registry), so signal every live native session to tear down too.
+    let native = crate::session_status::count();
+    crate::session_status::stop_all();
+    tracing::info!(
+        was_streaming,
+        native_sessions = native,
+        "management API: session stopped"
+    );
+    StatusCode::NO_CONTENT
+}
+
+/// Force a keyframe
+///
+/// Asks the encoder for an IDR frame on the active video stream (what a client requests
+/// after unrecoverable loss — exposed for debugging).
+#[utoipa::path(
+    post,
+    path = "/session/idr",
+    tag = "session",
+    operation_id = "requestIdr",
+    responses(
+        (status = ACCEPTED, description = "Keyframe requested"),
+        (status = UNAUTHORIZED, description = "Missing or invalid bearer token", body = ApiError),
+        (status = CONFLICT, description = "No active video stream", body = ApiError),
+    )
+)]
+pub(crate) async fn request_idr(State(st): State<Arc<MgmtState>>) -> Response {
+    let gs = st.app.streaming.load(Ordering::SeqCst);
+    let native = crate::session_status::count();
+    if !gs && native == 0 {
+        return api_error(StatusCode::CONFLICT, "no active video stream");
+    }
+    if gs {
+        st.app.force_idr.store(true, Ordering::SeqCst);
+    }
+    // Native sessions get the keyframe request through their registry flag (see `session_status`).
+    crate::session_status::force_idr_all();
+    StatusCode::ACCEPTED.into_response()
+}