Add stopped-workspace disk export and inspection

Finish the 3.1.0 secondary disk-tools milestone so stable workspaces can be
stopped, inspected offline, exported as raw ext4 images, and started again
without changing the primary workspace-first interaction model.

Add workspace stop/start plus workspace disk export/list/read across the CLI,
SDK, and MCP, backed by a new offline debugfs inspection helper and guest-only
validation. Scrub runtime-only guest state before disk inspection/export, and
fix the real guest reliability gaps by flushing the filesystem on stop and
removing stale Firecracker socket files before restart.

Update the docs, examples, changelog, and roadmap to mark 3.1.0 done, and
cover the new lifecycle/disk paths with API, CLI, manager, contract, and
package-surface tests.

Validation: uv lock; UV_CACHE_DIR=.uv-cache make check; UV_CACHE_DIR=.uv-cache
make dist-check; real guest-backed smoke for create, shell/service activity,
stop, workspace disk list/read/export, start, exec, and delete.

docs/install.md

@@ -85,7 +85,7 @@ uvx --from pyro-mcp pyro env list
 Expected output:
 
 ```bash
-Catalog version: 3.0.0
+Catalog version: 3.1.0
 debian:12 [installed|not installed] Debian 12 environment with Git preinstalled for common agent workflows.
 debian:12-base [installed|not installed] Minimal Debian 12 environment for shell and core Unix tooling.
 debian:12-build [installed|not installed] Debian 12 environment with Git and common build tools preinstalled.
@@ -159,6 +159,7 @@ This is the stable persistent-workspace contract:
 - `workspace snapshot *` and `workspace reset` make reset-over-repair explicit
 - `workspace diff` compares against the immutable create-time baseline
 - `workspace export` copies results back to the host
+- `workspace stop|start` and `workspace disk *` add secondary stopped-workspace inspection and raw ext4 export
 
 ## 6. Optional demo proof point
 
@@ -210,6 +211,7 @@ After the CLI path works, you can move on to:
 - baseline diff: `pyro workspace diff WORKSPACE_ID`
 - snapshots and reset: `pyro workspace snapshot create WORKSPACE_ID checkpoint` and `pyro workspace reset WORKSPACE_ID --snapshot checkpoint`
 - host export: `pyro workspace export WORKSPACE_ID note.txt --output ./note.txt`
+- stopped-workspace inspection: `pyro workspace stop WORKSPACE_ID`, `pyro workspace disk list WORKSPACE_ID`, `pyro workspace disk read WORKSPACE_ID note.txt`, and `pyro workspace disk export WORKSPACE_ID --output ./workspace.ext4`
 - interactive shells: `pyro workspace shell open WORKSPACE_ID`
 - long-running services: `pyro workspace service start WORKSPACE_ID app --ready-file .ready -- sh -lc 'touch .ready && while true; do sleep 60; done'`
 - localhost-published ports: `pyro workspace create debian:12 --network-policy egress+published-ports` and `pyro workspace service start WORKSPACE_ID app --ready-http http://127.0.0.1:8080/ --publish 18080:8080 -- ./start-app`
@@ -246,6 +248,11 @@ pyro workspace service status WORKSPACE_ID web
 pyro workspace service logs WORKSPACE_ID web --tail-lines 50
 pyro workspace service stop WORKSPACE_ID web
 pyro workspace service stop WORKSPACE_ID worker
+pyro workspace stop WORKSPACE_ID
+pyro workspace disk list WORKSPACE_ID
+pyro workspace disk read WORKSPACE_ID src/note.txt
+pyro workspace disk export WORKSPACE_ID --output ./workspace.ext4
+pyro workspace start WORKSPACE_ID
 pyro workspace logs WORKSPACE_ID
 pyro workspace delete WORKSPACE_ID
 ```
@@ -254,7 +261,7 @@ Workspace commands default to the persistent `/workspace` directory inside the g
 the identifier programmatically, use `--json` and read the `workspace_id` field. Use `--seed-path`
 when the workspace should start from a host directory or a local `.tar` / `.tar.gz` / `.tgz`
 archive. Use `pyro workspace sync push` for later host-side changes to a started workspace. Sync
-is non-atomic in `3.0.0`; if it fails partway through, prefer `pyro workspace reset` to recover
+is non-atomic in `3.1.0`; if it fails partway through, prefer `pyro workspace reset` to recover
 from `baseline` or one named snapshot. Use `pyro workspace diff` to compare the current workspace
 tree to its immutable create-time baseline, `pyro workspace snapshot *` to capture named
 checkpoints, and `pyro workspace export` to copy one changed file or directory back to the host. Use
@@ -268,7 +275,9 @@ service must be reachable from the host on `127.0.0.1`. Use `--secret` and `--se
 workspace creation when the sandbox needs private tokens or config, and
 `--secret-env SECRET_NAME[=ENV_VAR]` when one exec, shell, or service call needs that secret as an
 environment variable. Persisted secret files are available in the guest at
-`/run/pyro-secrets/<name>`.
+`/run/pyro-secrets/<name>`. Use `pyro workspace stop` plus `pyro workspace disk list|read|export`
+when you need offline inspection or one raw ext4 copy from a stopped guest-backed workspace, then
+`pyro workspace start` to resume it.
 
 ## Contributor Clone