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/i18n/locales/en/workflows.json

@@ -64,7 +64,7 @@
       "why": "When an aggregate chart flags a suspicious session, this is where you go to read exactly what happened, in order."
     },
     "lanes": {
-      "what": "Every stage record across all your lanes and their archived features, counted per pipeline node: how many times a stage was entered, passed, and how many of those passes left evidence behind.",
+      "what": "Every stage record across all your workspaces and their archived features, counted per pipeline node: how many times a stage was entered, passed, and how many of those passes left evidence behind.",
       "howToRead": "One row per node. The bar is scaled against the busiest node, split into green (passed with evidence), amber (passed but only claimed) and red (failed). The number on the right is passes / entries and the pass rate.",
       "why": "A node with a long amber bar is a stage everyone declares and nobody proves; a node that is never reached is a stage your pipeline does not really use."
     },
@@ -233,11 +233,11 @@
     "sortedByCompaction": " session(s) (sorted by compaction count)"
   },
   "lanes": {
-    "title": "Lane Pipeline Pass Rates",
+    "title": "Workspace Pipeline Pass Rates",
     "subtitle": "How often each stage of your own pipelines is actually passed",
     "pipelineLabel": "Pipeline template",
-    "laneLabel": "Lane",
-    "allLanes": "All lanes",
+    "laneLabel": "Workspace",
+    "allLanes": "All workspaces",
     "runs_one": "{{count}} run recorded",
     "runs_other": "{{count}} runs recorded",
     "legendEvidence": "passed with evidence",
@@ -245,8 +245,8 @@
     "legendFailed": "failed",
     "never": "never reached",
     "copyCommand": "Copy: {{command}}",
-    "empty": "No lane has recorded a stage yet. Create one with",
-    "emptyLane": "This lane has not recorded a stage yet.",
+    "empty": "No workspace has recorded a stage yet. Create one with",
+    "emptyLane": "This workspace has not recorded a stage yet.",
     "legendDetected": "reached, not declared",
     "detectedOnly": "detected ×{{count}}"
   },