Add print.rs (AmsState/AmsUnit/AmsTray/XcamSettings), fix print vs pushing

Mirrors continuum-schemas' schemas/bambulab/ restructuring: PushallResponse
removed (it never existed on the wire — pushall's request goes to
"pushing", but the state-push stream it triggers arrives under "print",
a different root key, not a direct reply). BambuReport::Pushing(...) ->
BambuReport::Print(PrintReport).

AmsTray is an untagged enum (Empty/Loaded) rather than one struct full of
Option<T> fields, matching the JSON Schema's oneOf for the same slot -
#[serde(deny_unknown_fields)] on EmptyTray is load-bearing: untagged enums
try variants in order, and a loaded tray (superset of Empty's one field)
would otherwise incorrectly match Empty first.

Verified against the full real ams/xcam example from the conversation via
examples/bambu_commands_demo.rs - both the empty and loaded tray in that
payload deserialize to the correct enum variant.

src/printer/bambu_commands/print.rs

@@ -0,0 +1,94 @@
+//! The ongoing print-state push (root key "print"). Doesn't carry a
+//! `CommandEnvelope` — no `sequence_id`/`command` seen on this one in the
+//! real capture, and it may genuinely not have them (an async push, not a
+//! reply to a specific request) — revisit if a real capture proves
+//! otherwise.
+
+#[derive(serde::Deserialize, Debug)]
+pub struct PrintReport {
+    pub ams: Option<AmsState>,
+    pub ams_exist_bits: Option<String>,
+    pub insert_flag: Option<bool>,
+    pub power_on_flag: Option<bool>,
+    pub tray_exist_bits: Option<String>,
+    pub tray_is_bbl_bits: Option<String>,
+    pub xcam: Option<XcamSettings>,
+    pub xcam_status: Option<String>,
+    // The real payload has a lot more fields than shown here (this
+    // example was truncated) — add them the same way, one field per line,
+    // `Option<T>` for anything that isn't always present.
+}
+
+/// Bambu's own naming has the outer container and the inner array both
+/// called `ams` — `print.ams.ams`, not a typo here, just what the printer
+/// actually sends.
+#[derive(serde::Deserialize, Debug)]
+pub struct AmsState {
+    pub ams: Vec<AmsUnit>,
+}
+
+/// One physical AMS unit (Bambu's numbering starts at 0 via `id`).
+#[derive(serde::Deserialize, Debug)]
+pub struct AmsUnit {
+    pub humidity: String,
+    pub id: String,
+    pub temp: String,
+    pub tray: Vec<AmsTray>,
+}
+
+/// A tray slot is either empty (just `id`) or loaded (the full field set)
+/// — two genuinely different shapes, not one shape with optional fields,
+/// so this is an untagged enum rather than a struct full of `Option<T>`.
+/// `#[serde(deny_unknown_fields)]` on `Empty` is load-bearing: untagged
+/// enums try variants in order, and without it a *loaded* tray (which has
+/// every field `Empty` allows, plus more) would incorrectly match `Empty`
+/// first, since a plain struct doesn't reject extra fields by default.
+/// Verified this the hard way — see git history.
+#[derive(serde::Deserialize, Debug)]
+#[serde(untagged)]
+pub enum AmsTray {
+    Empty(EmptyTray),
+    Loaded(LoadedTray),
+}
+
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct EmptyTray {
+    pub id: String,
+}
+
+#[derive(serde::Deserialize, Debug)]
+pub struct LoadedTray {
+    pub id: String,
+    pub bed_temp: String,
+    pub bed_temp_type: String,
+    pub cols: Vec<String>,
+    pub drying_temp: String,
+    pub drying_time: String,
+    pub nozzle_temp_max: String,
+    pub nozzle_temp_min: String,
+    pub remain: i32,
+    pub tag_uid: String,
+    pub tray_color: String,
+    pub tray_diameter: String,
+    pub tray_id_name: String,
+    pub tray_info_idx: String,
+    pub tray_sub_brands: String,
+    pub tray_type: String,
+    pub tray_uuid: String,
+    pub tray_weight: String,
+    pub xcam_info: String,
+}
+
+/// Camera-based AI print monitoring settings (spaghetti detection,
+/// first-layer inspection, etc.).
+#[derive(serde::Deserialize, Debug)]
+pub struct XcamSettings {
+    pub allow_skip_parts: bool,
+    pub buildplate_marker_detector: bool,
+    pub first_layer_inspector: bool,
+    pub halt_print_sensitivity: String,
+    pub print_halt: bool,
+    pub printing_monitor: bool,
+    pub spaghetti_detector: bool,
+}