feat: workspace aliases, tab groups of split panes, native path picker (v2.1.0)

- /api/workspaces and `agenthub workspace(s)` / `--workspace` as aliases of
  /api/lanes and `agenthub lanes` / `--lane`; old names print one stderr note.
  REPL `help lanes|workspace|workspaces` resolves through the aliases.
- A workspace holds up to ten sessions (slots 0-9); every console tab is a
  group of 1-4 split panes (PaneGroups, agenthub.workspace.paneLayout);
  parseGroups keeps the stored active tab when an earlier one is dropped.
- Browse button beside path fields: POST /api/lanes/pick-path opens the OS
  picker on the server's desktop — loopback only and no forwarding header
  (EREMOTE), a display failure is ENODIALOG not a Cancel, the dialog is
  killed when the request closes, a folder field falls back to the in-app
  browser on any failure.
- Changes rail counts chip, image viewer (/git/raw), status bar session
  counts and per-day cost (`date=` on /api/pricing/cost).
- /agenthub-open and /agenthub-doctor run from the INSTALLED build
  (supersededBy), doctor offers fixes behind two confirmations; plugin-open
  treats a locked bootstrap as non-fatal.
- New-terminal shell waits for the first attach (issue #55).
- repo-onboarding / debug-live-issue skills removed.
- OpenAPI: pick-path, lane/date on /pricing/cost, tool on /run/history,
  /api/workspaces mount.

.agents/skills/repo-onboarding/SKILL.md

@@ -1,20 +0,0 @@
----
-name: repo-onboarding
-description: Understand this repository quickly before making changes. Use for architecture discovery, ownership mapping, command selection, and initial implementation planning.
----
-
-# Repo Onboarding Skill
-
-## Workflow
-- Read `AGENTS.md`, `README.md`, and `ARCHITECTURE.md`.
-- Determine target layer: `server/`, `client/`, or docs.
-- Identify the minimal file set needed for the task.
-- Select verification commands before editing.
-
-## Verification defaults
-- Backend: `npm run test:server`
-- Frontend: `npm run test:client`
-
-## References
-- `references/module-map.md`
-- `references/verification-map.md`

.agents/skills/repo-onboarding/agents/openai.yaml

@@ -1,4 +0,0 @@
-interface:
-  display_name: "Repo Onboarding"
-  short_description: "Map architecture, ownership, and verification strategy before coding."
-  default_prompt: "Use repo-onboarding to analyze scope, affected modules, and validation commands for this task."

.agents/skills/repo-onboarding/references/module-map.md

@@ -1,8 +0,0 @@
-# Module Map
-
-- `server/index.js`: app startup and route mounting.
-- `server/routes/*.js`: API contracts and route behavior.
-- `server/db.js`: schema and statement layer.
-- `server/websocket.js`: live update broadcast path.
-- `client/src/pages/`: route-level UI.
-- `client/src/components/`: reusable UI primitives.

.agents/skills/repo-onboarding/references/verification-map.md

@@ -1,8 +0,0 @@
-# Verification Map
-
-- Backend changes:
-  - `npm run test:server`
-- Frontend changes:
-  - `npm run test:client`
-- Docs-only changes:
-  - validate command consistency against root `package.json`