fix: take the launcher window out of the shot when snipping

The snip was selecting a region around the launcher panel sitting in the
middle of the screen. `activateEntrypoint` calls `showWindow()` when it
activates a command from a closed launcher, so a view command's window is
already up before any extension code runs. Capturing from inside the chat
view could never have worked.

- `snip` is now a `no-view` command. It calls `closeMainWindow()` first,
  waits out the 50ms hide that `ui-service.hpp` schedules, then captures
  with nothing on screen, then brings the window back by launching `chat`
  with the file. `settleWindow()` exists because a capture started the
  instant the close resolves could still find the window there.
- The chat's action no longer captures inline. It launches `snip` and
  passes the session id, so there is one capture path, one capability
  check, and one place that deals with the window.
- The hand-off relays through `snip` rather than going straight back to
  `chat` on purpose: `ActivateEntrypointOptions::toggleIfAlreadyActive`
  defaults to true, so launching the *already active* view command closes
  the window instead of reopening it. A launch cannot override that flag,
  but relaying through a different no-view command makes the toggle branch
  unreachable.
- The action is hidden while streaming, since the hand-off unloads the
  view and would abandon an answer mid-sentence.
- Vision is settled before the selector appears, so a model that cannot
  read images never costs a selection gesture. `no` and `unknown` get
  different HUD wording.
- `lib/snip.ts` holds the hand-off contract; `lib/hooks/useSnip.ts` is
  gone, as nothing captures from a view any more.

Verified: 252 tests, tsc, eslint, prettier, and vici build. The deployed
manifest now reports `snip mode=no-view`.

package.json

@@ -19,8 +19,8 @@
       "name": "snip",
       "title": "Snip to Lam",
       "subtitle": "Lam Agent",
-      "description": "Capture a region of the screen and start a new chat about it. Offered only when the model in preferences supports image input, so check with \"Set Up Lam Agent\" if the shortcut seems to do nothing.",
-      "mode": "view"
+      "description": "Capture a region of the screen and start a new chat about it. The launcher window closes first so it cannot end up in the shot. Offered only when the model in preferences supports image input.",
+      "mode": "no-view"
     },
     {
       "name": "sessions",