Tell the user when the scene is drawn without a GPU

A day of pan/zoom that had suddenly become unusable on a 1.2M-entity
drawing turned out to be no regression at all: an unattended NVIDIA
userspace update had been applied without a reboot, the Vulkan ICD could
no longer talk to the still-loaded kernel module, and wgpu silently fell
through to Mesa's llvmpipe. Nothing in the app said so. iced picks the
adapter and names it only under RUST_LOG, so the only evidence was 32
`llvmpipe-N` threads in /proc. The same silence covers WARP on Windows,
SwiftShader in browsers, and the case where wgpu finds no adapter at all
and iced quietly draws the chrome with tiny-skia while the shader widget
is dropped, leaving a blank viewport. This commit makes all of that
visible, on every platform, without new dependencies.

Detection (src/scene/pipeline/mod.rs)
-------------------------------------
`GpuStatus` is derived from two signals:

* `record_gpu_adapter`, run from `MultiPipeline::new` (once per device,
  next to the existing uncaptured-error handler), reads
  `Device::adapter_info()`, prints one `[gpu] adapter: <name> (<backend>,
  <device type>, driver …)` line — stderr natively, `console.warn` on the
  web, which has no stderr — and keeps a copy.
* `note_scene_draw`, run from `ViewportPane::draw`, counts how often the
  viewport asked for a primitive. Every renderer makes that call; only
  wgpu goes on to `prepare` and create a device. Three draws with no
  device ever recorded therefore mean the primitive is being dropped.

The verdict is one of `Unknown`, `Hardware`, `Software(adapter)` or
`NoRenderer`. `Software` is `DeviceType::Cpu` — what Vulkan reports for
llvmpipe, DX12 for WARP and GL for a renderer string that gives it away —
plus a name match on the fallbacks browsers expose (SwiftShader, llvmpipe,
lavapipe, "Microsoft Basic Render"), because the WebGPU backend reports
every adapter as `Other` (gfx-rs/wgpu#8819). Metal has no software device,
so on macOS only `NoRenderer` can occur (a VM without a GPU); it is caught
by the draw count like everywhere else.

`gpu_status_if_changed` costs one atomic load per app message: a
generation counter moves only when a device is recorded or the draw count
crosses its threshold, so the app re-derives the verdict a handful of
times per session.

Notification (src/app/startup.rs, view/modal.rs, ui/statusbar)
-------------------------------------------------------------
`refresh_gpu_status` runs after every message. On a degraded verdict it
speaks through three channels, because many users never read the command
line:

* A popup, `ModalKind::GpuWarning`, queued once per verdict through the
  startup-modal queue so it waits its turn behind the file open. It names
  the adapter, states the consequence (slow navigation, unstable or
  missing rendering) and gives the remedy that usually applies on the
  running platform: a driver update not yet followed by a reboot on
  Linux, a missing driver or a Remote Desktop / VM session on Windows, a
  VM without a Metal device on macOS, hardware acceleration switched off
  in the browser. "Don't show again for this device" stores
  `GpuStatus::identity()` in `settings.gpu_warning_silenced`; keying it by
  verdict means silencing "software rendering on llvmpipe" does not
  silence a later, different failure.
* A status-bar pill in the theme's warning colours, `⚠ Software rendering`
  or `⚠ No GPU renderer`. It is not a `StatusPill`, so it cannot be hidden,
  and it stays for the session; clicking it reopens the popup, silenced or
  not.
* A command-line entry through the new `CommandLine::push_warning`, which
  is styled like an error but deliberately does not touch `last_error` /
  `error_revision`: automation reads those to decide whether the command it
  just ran failed, and a graphics warning is not a failed command.

`subscription()` requests frames only while the verdict is `Unknown` on a
document tab (the Start page draws no viewport), so the probe costs one
frame on a working GPU, three on none, then stops.

Verification
------------
* Live on the machine that had the incident, with the Vulkan loader
  restricted to Mesa (`VK_DRIVER_FILES=…/lvp_icd.json WGPU_BACKEND=vulkan`):
  popup → OK → pill → click reopens; "Don't show again" → restart → pill
  only, no popup.
* `gpu_tests::the_adapter_is_reported_once_per_device` (ignored, needs an
  adapter) asserts the classification on a real device; it was run on both
  llvmpipe (`Cpu`) and an NVIDIA GT 1030 (`DiscreteGpu`).
* Unit tests cover the name heuristic, the verdict function, the identity
  rule, the warning text with an adapter name that itself contains
  parentheses and commas, the settings round trip and the command-line
  semantics. New strings are in all 21 locales as the `gpu` Fluent group.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/mod.rs

@@ -727,6 +727,14 @@ pub(super) struct OpenCADStudio {
     /// of OS windows).
     active_modal: Option<ModalKind>,
     pending_startup_modals: std::collections::VecDeque<ModalKind>,
+    /// What is drawing the scene, once the first frame has told us. Drives
+    /// the graphics warning (popup, status-bar pill, command line).
+    gpu_status: crate::scene::pipeline::GpuStatus,
+    /// The pipeline's status generation this app has already looked at.
+    gpu_status_generation: u64,
+    /// `GpuStatus::identity()` of the verdict whose popup the user silenced
+    /// with "Don't show again for this device". Persisted in the settings.
+    gpu_warning_silenced: String,
     /// Plot modal geometry preserved while the Plot Style editor is open as
     /// a child dialog. None means Plotstyle was opened directly (e.g. command).
     plotstyle_parent_plot_geometry: Option<(iced::Vector, iced::Vector)>,
@@ -1739,6 +1747,10 @@ pub enum ModalKind {
     /// Add / remove the annotation scales a single selected object has a
     /// per-object representation for.
     AnnoObjectScale,
+    /// The scene is drawn by a software rasterizer, or not at all: what that
+    /// means and what usually fixes it. Queued once per verdict; the status
+    /// bar's ⚠ pill reopens it.
+    GpuWarning,
 }
 
 /// A property group controlled by a layer state's restore mask.
@@ -2861,6 +2873,12 @@ pub enum Message {
     PropConstraintLinkClick(Vec<acadrust::Handle>),
     // ── About window ────────────────────────────────────────────────────
     AboutOpen,
+    // ── Graphics warning ────────────────────────────────────────────────
+    /// The status bar's ⚠ pill: reopen the graphics warning.
+    GpuWarningOpen,
+    /// "Don't show again for this device": close the warning and remember
+    /// the verdict it described, so only a different one prompts again.
+    GpuWarningSilence,
     /// Close whatever in-canvas modal dialog is open (Plan B).
     CloseModal,
     // ── Attribute editor dialog ───────────────────────────────────────────
@@ -3613,6 +3631,9 @@ impl OpenCADStudio {
             recent_colors: Vec::new(),
             active_modal: None,
             pending_startup_modals: std::collections::VecDeque::new(),
+            gpu_status: crate::scene::pipeline::GpuStatus::Unknown,
+            gpu_status_generation: 0,
+            gpu_warning_silenced: String::new(),
             plotstyle_parent_plot_geometry: None,
             find_replace: FindReplaceState::default(),
             aec_drop_acknowledged: false,