[Feature]: wsh layout save/load — serialize a workspace/tab to JSON and replay it

[qveys]

Feature description

Wave already persists saved workspaces (tabs, blocks, layouts) automatically. But there's no way to reproduce a workspace setup programmatically — no equivalent of tmuxinator, smug, or VS Code's code-workspace files.

Today, wsh run, wsh launch, wsh web open, wsh view each create blocks one at a time, but there's no compositional API to say "lay out this set of blocks in this configuration." wsh blocks list exposes block IDs but is read-only (wsh-reference#blocks).

As a user with multiple repos + a monitoring stack, I want a per-project layout file checked into the repo (or ~/.config/waveterm/layouts/) that I can replay with one command:

wsh layout apply ~/Git/my-supervision/.wave-layout.json

…and end up with the same tab/block tree every time, on every machine.

Implementation Suggestion

1. wsh layout save [<file>] — serialize the current tab (or --workspace, or --all) to JSON: tab metadata, layout tree, per-block meta (view, controller, cmd, cwd, connection, magnified, etc.). The internal layout system (docs) already has a tree representation — just expose it.
2. wsh layout apply <file> [--into-tab|--new-tab|--new-workspace] — recreate the tree, instantiating each block via the existing block-creation paths. Respect connection, cmd:cwd, cmd:initscript, etc. so connections.json + secrets are reused.
3. JSON schema + json-schema entry in the same way widgets.json and connections.json get autocomplete (v0.11.1 release notes).
4. Optional: widgets.json widgets that point at a layout file ("view": "layout") so a single-click button restores a whole tab tree.

Anything else?

This composes beautifully with existing features:

• term:durable: true per-block in the layout file → reproducible long-running setups.
• cmd:initscript entries already in connections.json → no duplication.
• A team can commit .wave-layout.json next to docker-compose.yml/Makefile to onboard new contributors with one command.

Closely related (but not duplicate): #1372 (env vars from another block), #2738 (CLI focus/switch tabs), #3196 (rename tabs via wsh), #2106 (set window title via wsh). Those are individual primitives; this issue is about the composition layer on top.