fix(run,lanes): prompt autocomplete, per-lane Active runs, compact Changes header

- The run form's prompt box offers suggestions again: `/` lists the run
  cwd's project and user commands and skills plus the CLI built-ins
  (claude lanes only), `@` lists files under the cwd; Enter picks while
  the list is open and sends otherwise. The 2f39f4e rewrite had left a
  bare textarea that ignored both.
- Active runs lists only the current lane's runs and external sessions
  (sessions matched to the lane by longest path-boundary cwd), instead of
  every lane's.
- The Changes panel's git line and its actions are one compact row in one
  card, and the mode/range toolbar is one wrapping row.
- The lane card hides itself when it has nothing to show, instead of
  leaving an empty frame where the git row used to be.

client/src/pages/Workspace.tsx

@@ -874,7 +874,8 @@ export function Workspace() {
             )}
             {currentLane && showInfo && (
               <div className="max-h-[45vh] shrink-0 overflow-y-auto">
-                <div className="mb-3">
+                {/* No margin when the card rendered nothing (see LaneCard). */}
+                <div className="mb-3 has-[>div:empty]:mb-0">
                   <LaneCard
                     lane={currentLane}
                     onAction={(a, b) => handleLaneAction(currentLane.id, a, b)}

client/src/pages/__tests__/__snapshots__/screens.snapshot.test.tsx.snap

@@ -5570,11 +5570,16 @@ exports[`screen snapshots > Run 1`] = `
                   >
                     Prompt
                   </label>
-                  <textarea
-                    class="w-full bg-surface-2 border border-border rounded-md px-3 py-2 text-[11px] font-mono text-fg-primary placeholder:text-fg-muted focus:outline-none focus:border-accent/50 resize-none"
-                    placeholder="Ask Claude anything…"
-                    rows="5"
-                  />
+                  <div
+                    class="relative"
+                  >
+                    <textarea
+                      class="w-full bg-surface-2 border border-border rounded-md px-3 py-2 text-[11px] font-mono text-fg-primary placeholder:text-fg-muted focus:outline-none focus:border-accent/50 resize-none"
+                      placeholder="Ask Claude anything…"
+                      rows="5"
+                      spellcheck="false"
+                    />
+                  </div>
                   <div
                     class="mt-1 text-[10px] text-fg-muted"
                   >