feat(maestro): confirm every kill in the web client

The TUI has always raised `KillConfirm` before `x` kills anything; the web
sent `DELETE /api/sessions/:id` on the first press and only prompted when the
daemon refused. The command bar puts both behind the same three keystrokes,
so the difference now reads as a bug (#160).

The web follows the TUI: a kill is destructive and unattended agents live in
these sessions. `killDialog.ts` grows a confirmation that shares the force
prompt's shell, names the blockers the card already knows about, and keeps the
focus on Cancel. The guarded refusal still opens its own dialog behind it.

docs/COMMAND-BAR.md

@@ -158,12 +158,12 @@ searchable — the query line keeps working, now over those actions.
   ambiguous.
 - Escape, or backspace at an empty query, returns to the result list **with the
   previous query intact**. Drilling in and backing out is free.
-- Each action raises the flow it already has: kill goes through the existing
-  confirm-and-blockers dialog (`docs/WORKTREES.md`), rename through the
-  existing prompt pre-filled with the session's own name
-  (`docs/SIDEBAR.md`), spawn similar through the spawn form seeded from the
-  session's directory and command. The bar picks the action; it never
-  reimplements one.
+- Each action raises the flow it already has: kill through the confirmation
+  both clients ask for (`docs/SIDEBAR.md`) and the blockers dialog behind it
+  (`docs/WORKTREES.md`), rename through the existing prompt pre-filled with the
+  session's own name (`docs/SIDEBAR.md`), spawn similar through the spawn form
+  seeded from the session's directory and command. The bar picks the action; it
+  never reimplements one.
 
 No actions beyond those three, and no action across more than one session.
 

docs/SIDEBAR.md

@@ -316,7 +316,7 @@ Everything else is the same key on both clients:
 | `Tab`   | hand the keyboard to the pane               |
 | `c`     | collapse or expand the highlighted folder   |
 | `r`     | rename the highlighted session              |
-| `x`     | kill the highlighted session                |
+| `x`     | kill the highlighted session (confirms)     |
 | `n`     | open the spawn form                         |
 | `N`     | spawn with every default resolved           |
 | `?`     | show the shortcut overlay                   |
@@ -324,3 +324,18 @@ Everything else is the same key on both clients:
 The TUI binds these through its keymap, so a user can rebind any of them; the
 web client's are fixed. A binding added to one client belongs in this table and
 in both help overlays.
+
+## Killing a session
+
+**Every kill confirms first, in both clients** (#160). A kill is destructive
+and unattended agents live in these sessions, so neither client sends
+`DELETE /api/sessions/:id` off a single press. The TUI raises
+`OverlayKind::KillConfirm` (`[y]`/`[n]`); the web raises the same dialog its
+`✕` button and the command bar's action page both use. Cancel holds the focus
+in the web's dialog, so nothing kills on a stray Enter.
+
+The confirmation names what the card last saw in the way, when anything was —
+the daemon will refuse an unforced kill over such a worktree, and saying so
+before the attempt is cheaper than a refusal. What comes back from that refusal
+is a second, separate prompt offering `force=true`; `docs/WORKTREES.md` owns
+what a forced kill leaves behind.