feat: reveal all hidden shapes with Shift+H, release SAM3 VRAM on idle and on demand (REQ-191, REQ-192)

docs/requirements.md

@@ -276,6 +276,13 @@ changes.
   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.
+- **REQ-191** — `Shift+H` in the review editor toggles a **reveal-all overlay**: every hidden
+  shape — `H`-hidden shapes and shapes of hidden classes alike — is drawn on the canvas again
+  while nothing about what is actually hidden changes. A second `Shift+H` turns the overlay
+  off and the previous hidden state is back exactly as it was. While the overlay is on, the
+  "Shapes on this frame" panel shows a chip saying shapes are being revealed, and a plain `H`
+  drops an active overlay first instead of hiding anything, so from then on the keystroke
+  edits the real hidden state. Session-only, like the hide state itself.
 
 ## E4. Live counting preview
 
@@ -479,3 +486,13 @@ changes.
   folder has moved once already and everything in it must survive the next move), which
   strengthens the never-hardcoded rule of REQ-072. Training, preview, the batch job, model
   download and live counting all reach the same weights through this one resolution.
+- **REQ-192** — The SAM3 model's ~4 GB of VRAM is not held forever. After
+  `SAM3_IDLE_UNLOAD_S` seconds (default 1200 = 20 minutes; `0` never; an environment
+  variable, per REQ-072) without any SAM3 use, the model is released — through the same
+  release path training already uses (REQ-065) and under the same one-holder rule: a job or
+  an interactive assist in flight postpones the release to the next check, it is never
+  interrupted. `POST /api/sam3/release` frees it immediately instead of waiting, and answers
+  `409` while the GPU is busy. `/api/health`'s `model_loaded` field reports the state, and the
+  topbar badge shows `SAM3: Loaded` (green, clickable to release) / `SAM3: Idle` (not in VRAM,
+  loads on next use) / `SAM3: Off` (not enough free VRAM to load). The next call after a
+  release rebuilds the model from the local cache in about 12 seconds.