Reorder tabs by dragging, and pop the browser view into its own window

Two things the UI couldn't do: rearrange the tab strip, and watch the
browser while working somewhere else.

**Drag to reorder.** `moveTab`/`moveActiveTab` on the store, HTML5 drag on
the strip with a marker showing where the drop lands, `Ctrl+Shift+←/→` for
the same thing without a mouse. Reordering deliberately does not select
what it moves, so a drag aimed at a background tab doesn't yank the main
area away from a terminal mid-run. A tab being renamed is not draggable —
a draggable ancestor swallows the mouse-drag that selects text in its
input.

**Pop the browser view out.** `browser_view/popout.rs` opens the view's
existing token-bearing loopback URL as a second OS window, with a
"Keep on top" toggle so it can float above the app. Window-only: the
viewer, the proxy and the container are untouched, so popping out and
back interrupts nothing.

Three things it rests on:

- No capability lists that window, so it has no IPC surface — right for a
  page served out of a container, and it must stay that way.
- The app CSP is irrelevant to it: `frame-src` constrains what the app's
  document may *embed*, and this is a top-level document. The port range
  and the token gate are what actually protect it, unchanged.
- The window is owned by the session, so the supervisor's teardown closes
  it. A window onto a viewer that no longer exists is worse than none.

The pane drops its iframe while popped out — two viewers can both *drive*
the browser, and two cursors on one page is not a feature.

`lib.rs`'s `on_window_event` is now guarded on `label() == "main"`. It
fires for every window and its body stops every container and exits, so
without the guard closing a pop-out would quit the app.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

HOW-TO-USE.md

@@ -191,6 +191,11 @@ Anthropic-backend project uses that token without its own login. See
   terminal tab to rename it, jump to its project home, or close it; double-click to rename inline.
   There is no separate terminal tab bar and no "+" button — tabs appear when you open a project or
   a terminal.
+
+  **Drag a tab to reorder it.** A line shows where it will land, and dropping it does not change
+  which tab you are looking at — so you can rearrange the strip without pulling focus away from a
+  terminal that is mid-run. `Ctrl+Shift+←` and `Ctrl+Shift+→` move the *active* tab the same way
+  without the mouse. The order is per-session: it is not saved when you quit.
 - **Status indicators (top right)** — Docker connection and container image availability. Each pairs
   a coloured dot with a word, so status is never conveyed by colour alone. The **?** button opens
   the built-in help.
@@ -211,7 +216,7 @@ for selecting a project and for two quick controls that appear on hover — star
 Claude terminal. Everything else about a project lives in Project Home.
 
 The header shows the project name, its status, how long the container has been up, and the action
-buttons. Below that are five tabs:
+buttons. Below that are six tabs:
 
 | Tab | What it's for |
 |---|---|
@@ -220,6 +225,7 @@ buttons. Below that are five tabs:
 | **Automation** | The scheduled tasks running inside this container — see [Automation & Scheduled Tasks](#automation--scheduled-tasks) |
 | **Config** | All per-project configuration — see [Project Configuration](#project-configuration) |
 | **Files** | Browse, download and upload files inside the container |
+| **Browser** | Watch — and take over — the browser Claude is driving with Playwright, see [The Browser Tab](#the-browser-tab) |
 
 ### Sessions
 
@@ -257,6 +263,37 @@ included, and each tile opens a list of what it found.
 
 The counts are only available while the container is running.
 
+### The Browser Tab
+
+When Claude drives a browser with Playwright inside the container, the **Browser** tab shows you
+that browser live — and lets you take it over with your own mouse and keyboard.
+
+It is **off by default and opted into per project**, and it never installs anything on its own.
+Opening the tab only *probes* the container, so it can tell you what is missing before you ask for
+a view; installing Playwright and downloading a browser are separate, labelled buttons that state
+what they cost before you press them. See
+[What's Inside the Container](#whats-inside-the-container) for why the browser itself is not
+pre-installed.
+
+Press **Start browser view** and the pane fills with Playwright's own dashboard, running inside the
+container and reached over a token-gated listener on your machine's loopback address. Nothing is
+exposed off the machine.
+
+#### Watching it while you work
+
+Press **Open in own window** and the view moves out of the tab into a window of its own — put it on
+a second monitor, or turn on **Keep on top** and let it float above the app while you work in a
+terminal. This is a window change only: the browser and the view keep running throughout, so
+popping out and back costs nothing and interrupts nothing.
+
+While the view is in its own window the tab shows a placeholder rather than a second copy of it —
+two viewers would both be able to *drive* the browser, and two cursors on one page is not useful.
+**Put back in tab**, or just closing the window, brings it back.
+
+The window belongs to the view, not to the tab: closing the project's home tab leaves it open, and
+stopping the view — by pressing **Stop**, stopping the container, or removing the project — closes
+it, because a window showing a viewer that no longer exists is worse than no window.
+
 ---
 
 ## Project Management
@@ -1119,6 +1156,7 @@ triple-c-scheduler add --name "test" --schedule "0 */6 * * *" --prompt "Run test
 | **Ctrl+Tab** | Switch to the next tab |
 | **Ctrl+Shift+Tab** | Switch to the previous tab |
 | **Ctrl+1** … **Ctrl+9** | Jump to the first through ninth tab |
+| **Ctrl+Shift+←** / **Ctrl+Shift+→** | Move the active tab one place along the strip (the mouse equivalent is dragging it) |
 
 > **Why Ctrl+Shift+W and not Ctrl+W?** `Ctrl+W` is readline's `kill-word` — it deletes the word
 > before the cursor, and it is used constantly in the terminal this app is built around. Binding it