feat: one-click copy of effective auto-annotate params (REQ-186)

- ClassParamsTable: Copy button above per-class overrides table —
  clipboard text, one line per class (class/conf/iou/minbox/container),
  effective values (override else global), present in both the
  per-batch and mass auto-annotate modals via the shared component
- clipboard.js: extract legacyCopy + copyText from ArchiveControls
  (insecure-context execCommand fallback), ArchiveControls now imports it
- docs: REQ-186 added; design/ui-spec/tasks synced

docs/ui-spec.md

@@ -462,6 +462,12 @@ Two columns inside one dialog (920 px wide, max 96 vw / 90 vh, scrollable).
   unmarked classes are governed by IoU alone. Toggling is optimistic
   `PATCH /projects/{id} { containers: { [classId]: bool } }` into `project_classes.container`
   with revert on rejection — preview and batch job read the same stored flag.
+- **Copy (REQ-186)** — small right-aligned ghost button above the overrides table; label
+  `Copy`, flips to `Copied` for 1.5 s inside an `aria-live` span, and on failure silently
+  stays `Copy`. One line per selected class, e.g.
+  `class sack conf 0.4 iou 0.6 minbox 0.005 container false` — an empty input copies the
+  global value. Present in the engine-chooser modal **and** the mass modal (shared
+  component).
 - `ClassPromptPanel`:
   - Target-class chips. Without SAM3 a chip is a simple toggle.
   - **With SAM3 a chip is two buttons**: the *name* selects-and-activates, the `×` deselects.