Per-shape hide + dimmed shape list in review editor (REQ-185, amended REQ-183)

- ReviewPage: hiddenShapeIds/overriddenShapeIds session Sets, H toggles
  selected/marked shapes, purge effect removed (dimmed rows selectable
  from list), auto-override on draw/assist/copy into hidden class,
  class-eye toggle clears that class's overrides
- ReviewSidebar: all rows listed, dimmed rows get restore eye, header
  count = total shapes
- ShortcutsPanel: H entry
- docs: REQ-183 amended + REQ-185 added; design/ui-spec/tasks synced

docs/requirements.md

@@ -186,11 +186,12 @@ changes.
   the **current frame only** (REQ-046 stays batch-wide). One click, no confirmation dialog;
   the next frame is untouched.
 - **REQ-183** — In the manual review editor, each class row has a **hide toggle**. A hidden
-  class's shapes disappear from both the annotation canvas and the "Shapes on this frame"
-  list — not selectable, not marquee-selectable, not deletable while hidden — while the class
-  row keeps its real per-frame count and its eye state, so what is hidden stays visible as
-  state. The choice is session state: it survives frame changes, resets when the review page
-  is left, and never touches stored data.
+  class's shapes are never drawn on the annotation canvas — not clickable there, not
+  marquee-selectable — but they stay listed in "Shapes on this frame", dimmed, each dimmed
+  row carrying an eye that restores it individually (REQ-185). The class row keeps its real
+  per-frame count and its eye state, so what is hidden stays visible as state. The choice is
+  session state: it survives frame changes, resets when the review page is left, and never
+  touches stored data.
 - **REQ-184** — A class can be marked as **container** (persisted on
   `project_classes.container`, edited next to the per-class overrides in the auto-annotate
   modals). When the cross-class NMS of REQ-031 compares another class's box against a
@@ -198,6 +199,16 @@ changes.
   the smaller box's area lies inside the container's box, both survive. The flag changes
   nothing else — unmarked classes are governed by IoU alone — and preview and batch job
   read the same stored flag.
+- **REQ-185** — In the manual review editor, the `H` key toggles hide on every currently
+  selected shape (the single selection, or all marked shapes in select mode). Hiding is per
+  shape: a shape hidden by `H`, and a shape hidden only because its class is hidden, both
+  stay listed in "Shapes on this frame" **dimmed**, where an eye button restores it — the
+  eye first un-hides an `H`-hidden shape, otherwise it overrides the class hide. Dimmed rows
+  remain selectable, reclassable and deletable from the list; they are simply never drawn
+  on the canvas. Shapes created while their class is hidden (draw, assist, copy) are
+  auto-overridden so the user sees what they just made. Like the class eye, this is session
+  state: it survives frame changes, resets when the review page is left, and never touches
+  stored data.
 
 ## E4. Live counting preview