Merge PR #2077: LR-BEHAV-BG-TASKS: one progress bar, spinner and busy button

# Conflicts:
#	crates/ui-egui/src/lib.rs
#	docs/whats-new.md

docs/parity-checklist.md

@@ -461,7 +461,7 @@ differences and missing bindings are in [ui-parity.md](ui-parity.md#shortcuts).
 | LR-BEHAV-BATCH | Batch apply to selection | P0 | ✅ | `cmd:photo.rate`, `cmd:develop.paste`, `cmd:preset.apply`, `cmd:app.export` | |
 | LR-BEHAV-PREVIEW-HOVER | Hover previews | P1 | ✅ | `crates/ui-egui/src/panels/presets.rs`, `crates/ui-egui/src/panels/profiles.rs`, `crates/ui-egui/src/panels/right.rs` (`versions`), `crates/ui-egui/src/panels/detail.rs` | presets, profile menu, profile browser and versions preview in the loupe |
 | LR-BEHAV-PROGRESSIVE | Progressive rendering | P0 | ✅ | `crates/engine/src/media.rs`, `crates/preview/src/lib.rs` | |
-| LR-BEHAV-BG-TASKS | Background tasks | P0 | ✅ | `cmd:activity.list`, `cmd:activity.cancel`, `crates/engine/src/activity.rs`, `crates/ui-egui/src/panels/activity.rs`, `docs/background-tasks.md`, `crates/preview/src/lib.rs` (`JobPool`) | renders off the UI thread; exports run several photos of a batch side by side (`export_parallelism`, memory-gated; files, names and order as one at a time, #496); one activity stack in the top-left corner under the top bar, as in Lightroom Classic (issue #345): imports, folder scans, exports (and the contact sheet PDF), Synchronize Folder (its scan and its run), Build / Smart Previews, Lightroom catalog inspect / import, Photo Merge, model downloads (SAM 3, face, AI Denoise), the face scan, AI Denoise, Find Missing Photos and Reload from Disk (`cmd:photo.reload`, its files decoded on a worker thread, cancellable; `wait: true` for agents) each show a row (name, progress bar or a sweep while the amount isn't known, count and current item) once 0.5 s old, three rows then "+N more"; ✕ cancels the jobs that can stop ("Stopping…" until they do); quitting asks while a cancellable task runs; agents and `ui.inspect` (`activity`) see the same list. No pause (Lightroom can pause some tasks) |
+| LR-BEHAV-BG-TASKS | Background tasks | P0 | ✅ | `cmd:activity.list`, `cmd:activity.cancel`, `crates/engine/src/activity.rs`, `crates/ui-egui/src/panels/activity.rs`, `crates/ui-egui/src/progress.rs`, `docs/background-tasks.md`, `crates/preview/src/lib.rs` (`JobPool`) | renders off the UI thread; exports run several photos of a batch side by side (`export_parallelism`, memory-gated; files, names and order as one at a time, #496); one activity stack in the top-left corner under the top bar, as in Lightroom Classic (issue #345): imports, folder scans, exports (and the contact sheet PDF), Synchronize Folder (its scan and its run), Build / Smart Previews, Lightroom catalog inspect / import, Photo Merge, model downloads (SAM 3, face, AI Denoise), the face scan, AI Denoise, Find Missing Photos and Reload from Disk (`cmd:photo.reload`, its files decoded on a worker thread, cancellable; `wait: true` for agents) each show a row (name, progress bar or a sweep while the amount isn't known, count and current item) once 0.5 s old, three rows then "+N more"; ✕ cancels the jobs that can stop ("Stopping…" until they do); quitting asks while a cancellable task runs; agents and `ui.inspect` (`activity`) see the same list. No pause (Lightroom can pause some tasks) |
 | LR-BEHAV-OFFLINE | Offline editing | P1 | ✅ | | local-first: everything works offline |
 | LR-BEHAV-WEB-SAFETY | Library safety in the browser build | P1 | 🟡 | `cmd:file.backupLibrary`, `cmd:file.restoreLibrary`, `apps/lightcraft-web/src/safety.rs`, `apps/lightcraft-web/src/backup.rs`, `apps/lightcraft-web/src/files.rs` | web only (experimental): Back Up Library (zip of the catalog and every stored original) and a non-destructive Restore; failed saves show as unsaved and are retried; a photo that can't be stored isn't added; one tab per library (Web Locks); notices for storage that isn't persistent and for a library that can't open; `?reset` asks first; a panic shows a message. Missing: `?safe` start, deleting originals of removed photos, zip64 (backups > 4 GB) |
 | LR-BEHAV-GPU | GPU acceleration | P0 | ✅ | `crates/gpu/src/render.rs`, `cmd:app.gpu`, `docs/gpu-pipeline.md`, `crates/ui-egui/src/panels/notices.rs` | CPU fallback per render on device limits, out of memory, device errors / loss, incomplete or black results (`perf.gpuReason`, `perf.gpuFallback`; each render reports its own reason — `lightcraft_gpu::try_render`, `gpuFallback` per exported file — issue #675); short submissions for slow iGPUs; backend choice (DX12 only on Windows, `LIGHTCRAFT_GPU_BACKEND` / `WGPU_BACKEND`), device created after the window opens, crash sentinel (issue #136); a GPU lost while LightCraft runs (driver reset) stops it with that message and turns GPU rendering off for the next start, which says why (issue #1337; the window's renderer can't survive the lost device); quitting waits (up to 2 s) for renders in flight and starts no new GPU work, so none is inside the driver when the process exits (`crates/gpu/src/exit.rs`, issue #620; seen crashing only on Linux + NVIDIA, other drivers unverified); with GPU rendering on and no adapter found at all (e.g. no Vulkan loader on NixOS outside `nix develop`), the desktop app says once per session that it renders on the CPU and points to Help ▸ System Info (`gpu_notice`; not when the GPU is turned off or only a software adapter exists); no tiling beyond the buffer limit (CPU) |
@@ -927,3 +927,4 @@ Latin stays upright. Advanced Japanese composition remains open. Regression cove
 | 2026-10-16 | minor | LR-VIEW-PHOTOGRID: when the photos shown change by those an edit touched (an import's batch, a capture time, a crop), the grid reads only those photos' dates and shapes again instead of every photo of the list (a 16-photo batch at 181,749 photos: grid frame 101 ms → 7 ms); status unchanged |
 | 2026-10-19 | minor | LRC-LIB-LIBFOLDERS: the sidebar trees indent by a narrower step (14 / 12 / 10 / 8 pt) when the deepest open row would not fit the panel, instead of cutting its name or scrolling sideways at once (issue #2298); status unchanged (✅) |
 | 2026-10-15 | patch | LR-EXP-DIM: Width & Height (`fit: widthHeight`) limits the width and the height as the photo stands, beside Dimensions (W × H, either orientation), as in Lightroom (#1620); status unchanged (✅) |
+| 2026-10-16 | patch | LR-BEHAV-BG-TASKS: progress bars and spinners come from one component (`progress.rs`): the activity stack, model downloads, denoise and the face scan share it; busy buttons and a themed thumbnail placeholder added; status unchanged |

docs/whats-new.md

@@ -22,6 +22,12 @@
 - The stars in the bottom bar, the Info panel and the filter bar are now one shared control, and the badges on grid
   cells, filmstrip thumbnails and the Compare caption use the same drawing. Hovering a star in the filter bar now
   previews the rating like the others do, and with a star focused (Tab), ← and → lower and raise the rating.
+### Progress looks the same everywhere
+- Download, scan, denoise and activity progress now use one bar that fills the width it is given, with its text on
+  it, and a gentle sweep while the amount of work isn't known yet. Waits that only said "Selecting…", "Waiting to
+  start…" or "Installing…" now show a small turning arc beside the text, and a thumbnail still being made shows a
+  quiet placeholder that fits the theme in the grid, the filmstrip and Compare. Screen readers hear a progress
+  indicator with its percentage.
 
 ### Sharper resampling in HDR and panorama merges
 - Merged photos (HDR and panorama) are resampled with a sharper filter (Lanczos-3 instead of bilinear). Moving a