Fix unikernel deployment (#109)

This PR addresses an issue a user noticed where the instructions
resulted in a broken deployment.

### Issue
Instances based off the pushed image would do nothing but reboot as
shown by the logs. Of note the uploaded image was 37MB.

### Changes
* The primary fix is the addition of a flag specifying that the `initrd`
filesystem is EROFS.
* The headless image memory allocation is increased from 1024MB as it
was insufficient.
* Variables are added to `run-unikernel.sh` scripts that allow adjusting
the `volimport` path prefix and the VCPUS parameter.
* The `volimport` prefix environment variable might be unnecessary but
was preferred as the original references `onkernel`. The `official`
version seems to work and is the default.
* The README is improved.

Both headless and headful images were built and run. The headful image
ran with WebRTC enabled.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Package unikernels with EROFS, increase headless memory, add VCPUS and
VOLIMPORT_PREFIX envs, and refine README unikernel instructions.
> 
> - **Unikernel build**
> - Add `--rootfs-type erofs` to
`images/chromium-headless/build-unikernel.sh` and
`images/chromium-headful/build-unikernel.sh`.
> - **Unikernel run**
>   - `images/chromium-headless/run-unikernel.sh`:
>     - Memory: `-M` increased from `1024` to `3072`.
>     - vCPUs configurable via `VCPUS` (default `1`).
>   - `images/chromium-headful/run-unikernel.sh`:
>     - vCPUs configurable via `VCPUS` (default `4`).
> - Volume import image prefix configurable via `VOLIMPORT_PREFIX`
(defaults to `onkernel`).
> - **Docs**
> - `README.md`: Update Unikraft instructions—split secret exports, use
explicit `IMAGE=... images/.../{build,run}-unikernel.sh` commands, add
headful run alternative with `VOLIMPORT_PREFIX`, and note `VCPUS`
tunable.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
d390334. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: matthewjmarangoni

README.md

@@ -58,13 +58,16 @@ Alternatively, you can run the browser on a Unikraft unikernel.
 `curl -sSfL https://get.kraftkit.sh | sh`
 
 ### 2. Add Unikraft Secret to Your CLI
-`export UKC_METRO=<region> and UKC_TOKEN=<secret>`
+`export UKC_METRO=<region>`
+`export UKC_TOKEN=<secret>`
 
 ### 3. Build the image
-`./build-unikernel.sh`
+`IMAGE=YOUR_UKC_USERNAME/chromium-headless-test:latest images/chromium-headless/build-unikernel.sh`
 
 ### 4. Run it
-`./run-unikernel.sh`
+`IMAGE=YOUR_UKC_USERNAME/chromium-headless-test:latest images/chromium-headless/run-unikernel.sh`
+or
+`IMAGE=YOUR_UKC_USERNAME/chromium-headful-test:latest VOLIMPORT_PREFIX=official images/chromium-headful/run-unikernel.sh`
 
 When the deployment finishes successfully, the Kraft CLI will print out something like this:
 ```
@@ -91,6 +94,7 @@ Deployed successfully!
 - Various services (mutter, tint) take a few seconds to start-up. Once they do, the standby and restart time is extremely fast.
 - The Unikraft deployment generates a url. This url is public, meaning _anyone_ can access the remote GUI if they have the url. Only use this for non-sensitive browser interactions, and delete the unikernel instance when you're done.
 - You can call `browser.close()` to disconnect to the browser, and the unikernel will go into standby after network activity ends. You can then reconnect to the instance using CDP. `browser.close()` ends the websocket connection but doesn't actually close the browser.
+- VCPUS value can be adjusted using the variable: `VCPUS=8`
 
 ## Connect to the browser via Chrome DevTools Protocol
 

images/chromium-headful/build-unikernel.sh

@@ -31,6 +31,7 @@ echo "Image index/name: $UKC_INDEX/$IMAGE"
 kraft pkg \
   --name $UKC_INDEX/$IMAGE \
   --plat kraftcloud \
+  --rootfs-type erofs \
   --arch x86_64 \
   --strategy overwrite \
   --push \

images/chromium-headful/run-unikernel.sh

@@ -59,14 +59,14 @@ cat "$FLAGS_DIR/flags"
 kraft cloud volume rm "$volume_name" || true
 kraft cloud volume create -n "$volume_name" -s 16M
 # Import the flags directory into the freshly created volume
-kraft cloud volume import --image onkernel/utils/volimport:1.0 -s "$FLAGS_DIR" -v "$volume_name"
+kraft cloud volume import --image "${VOLIMPORT_PREFIX:-onkernel}/utils/volimport:1.0" -s "$FLAGS_DIR" -v "$volume_name"
 
 # Ensure the temp directory is cleaned up on exit
 trap 'rm -rf "$FLAGS_DIR"' EXIT
 
 
 deploy_args=(
-  --vcpus 4
+  --vcpus ${VCPUS:-4}
   -M 4096
   -p 9222:9222/tls
   -p 444:10001/tls

images/chromium-headless/build-unikernel.sh

@@ -32,5 +32,6 @@ kraft pkg \
   --plat kraftcloud \
   --arch x86_64 \
   --strategy overwrite \
+  --rootfs-type erofs \
   --push \
   .

images/chromium-headless/run-unikernel.sh

@@ -15,10 +15,10 @@ deploy_args=(
   --scale-to-zero idle
   --scale-to-zero-cooldown 3000ms
   --scale-to-zero-stateful
-  --vcpus 1
-  -M 1024
+  --vcpus ${VCPUS:-1}
+  -M 3072
   -e RUN_AS_ROOT="$RUN_AS_ROOT"
-  -e LOG_CDP_MESSAGES=true \
+  -e LOG_CDP_MESSAGES=true
   -p 9222:9222/tls
   -p 444:10001/tls
   -n "$NAME"