feat(ui): call lanes "workspaces" in the UI, CLI output and docs

Copy-only rename (workspace redesign, phase 0). The word a user reads
changes — "Lane" → "Workspace", "Add lane" → "Add workspace" — in both
locales, in agenthub CLI prose and help, in the server's error messages
and in the docs. Every identifier stays: /api/lanes, `agenthub lanes`,
--lane, AGENTHUB_LANE_ID, error codes, tmux names, DB tables, file,
component and i18n key names. docs/LANES.md keeps its name, retitled
"Workspaces (lanes)".

client/src/pages/__tests__/Workspace.test.tsx

@@ -499,7 +499,9 @@ describe("Workspace layout", () => {
     expect(strip.firstElementChild).toBe(screen.getByTestId("lane-tile-add"));
 
     await user.click(screen.getByTestId("lane-tile-add"));
-    expect(await screen.findByText("Create a lane from a working directory")).toBeInTheDocument();
+    expect(
+      await screen.findByText("Create a workspace from a working directory")
+    ).toBeInTheDocument();
   });
 
   it("gives every lane a tile in the carousel", async () => {

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

@@ -5428,12 +5428,12 @@ exports[`screen snapshots > Run 1`] = `
           <span
             class="block text-sm font-medium text-fg-primary"
           >
-            No lanes yet
+            No workspaces yet
           </span>
           <p
             class="mt-0.5 text-xs text-fg-muted"
           >
-            A lane is one working directory the dashboard follows — its pipeline, sessions and terminal. Click anywhere on this card to add one, or from a terminal:
+            A workspace is one working directory the dashboard follows — its pipeline, sessions and terminal. Click anywhere on this card to add one, or from a terminal:
              
             <code
               class="rounded bg-surface-2 px-1.5 py-0.5 text-[11px] text-fg-secondary"
@@ -5464,7 +5464,7 @@ exports[`screen snapshots > Run 1`] = `
               d="M12 5v14"
             />
           </svg>
-          Add lane
+          Add workspace
         </span>
       </button>
       <div
@@ -7324,7 +7324,7 @@ exports[`screen snapshots > Settings 1`] = `
               d="M18 9a9 9 0 0 1-9 9"
             />
           </svg>
-          Lanes
+          Workspaces
         </button>
         <button
           class="inline-flex items-center gap-1.5 text-xs whitespace-nowrap px-2.5 py-1.5 rounded-lg border transition-colors flex-shrink-0 border-border text-fg-secondary hover:text-fg-primary hover:bg-surface-3"
@@ -8339,12 +8339,12 @@ exports[`screen snapshots > Settings 1`] = `
             d="M18 9a9 9 0 0 1-9 9"
           />
         </svg>
-        Lanes
+        Workspaces
       </h3>
       <p
         class="text-xs text-fg-muted mb-4"
       >
-        Machine-wide lane housekeeping.
+        Machine-wide workspace housekeeping.
       </p>
       <div
         class="card p-5 space-y-4"
@@ -11029,7 +11029,7 @@ exports[`screen snapshots > Workflows 1`] = `
           <h2
             class="text-sm font-semibold text-fg-primary"
           >
-            Lane Pipeline Pass Rates
+            Workspace Pipeline Pass Rates
           </h2>
           <button
             aria-expanded="false"
@@ -11079,7 +11079,7 @@ exports[`screen snapshots > Workflows 1`] = `
           <p
             class="text-sm text-fg-muted"
           >
-            No lane has recorded a stage yet. Create one with
+            No workspace has recorded a stage yet. Create one with
              
             <code>
               agenthub lanes add --cwd $(pwd)