fixes panic when api returns nil (#50)

`kernel browsers list` panics when there are no browsers to list! Fixed
and added a unit test for it 😄

I also didn't like that prod release is 4 commands so I vibed a script
to do it


**Previously**
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x0 pc=0x1025be884]

goroutine 1 [running]:
github.com/onkernel/cli/cmd.BrowsersCmd.List({{0x1029b10c8, 0x140000d2300}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, ...}, ...)
	/Users/tanmaysardesai/github.com/onkernel/cli/cmd/browsers.go:222 +0x164
github.com/onkernel/cli/cmd.runBrowsersList(0x102e4a560, {0x10263262a?, 0x4?, 0x102632536?})
	/Users/tanmaysardesai/github.com/onkernel/cli/cmd/browsers.go:2128 +0x2ec
github.com/spf13/cobra.(*Command).execute(0x102e4a560, {0x102e80cc0, 0x0, 0x0})
	/Users/tanmaysardesai/go/pkg/mod/github.com/spf13/[email protected]/command.go:1015 +0x7d4
github.com/spf13/cobra.(*Command).ExecuteC(0x102e4ece0)
	/Users/tanmaysardesai/go/pkg/mod/github.com/spf13/[email protected]/command.go:1148 +0x350
github.com/spf13/cobra.(*Command).Execute(...)
	/Users/tanmaysardesai/go/pkg/mod/github.com/spf13/[email protected]/command.go:1071
github.com/spf13/cobra.(*Command).ExecuteContext(...)
	/Users/tanmaysardesai/go/pkg/mod/github.com/spf13/[email protected]/command.go:1064
github.com/charmbracelet/fang.Execute({0x1029ae0f8, 0x102e80cc0}, 0x102e4ece0, {0x14000223e98, 0x2, 0x2?})
	/Users/tanmaysardesai/go/pkg/mod/github.com/charmbracelet/[email protected]/fang.go:151 +0x320
github.com/onkernel/cli/cmd.Execute({{0x10285b4f8, 0x6}, {0x10285bce0, 0x28}, {0x10285bb50, 0x14}, {0x10285ba98, 0x8}})
	/Users/tanmaysardesai/github.com/onkernel/cli/cmd/root.go:164 +0x2e8
main.main()
	/Users/tanmaysardesai/github.com/onkernel/cli/cmd/kernel/main.go:17 +0x78
```

**now**
```
 INFO  No running browsers found
```

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Prevents a panic in `kernel browsers list` when the API returns no
page, adds a unit test, and introduces a `scripts/release.sh` with
updated release docs.
> 
> - **CLI (browsers list)**
> - Safely handle `nil` page from SDK in `cmd/browsers.go` and treat as
empty results.
>   - JSON output now prints `[]` when no items (`len(browsers)==0`).
>   - Shows "No running browsers found" when empty instead of panicking.
> - **Tests**
> - Add `TestBrowsersList_PrintsEmptyMessagePageIsNil` in
`cmd/browsers_test.go`.
> - **Release**
> - Add `scripts/release.sh` to tag, push, and run `make release` with
basic version validation.
> - Update `DEVELOPMENT.md` to use `git describe --abbrev=0` and
`./scripts/release.sh <version> [description]` for releases.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
fe327db. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: tnsardesai

DEVELOPMENT.md

@@ -78,9 +78,6 @@ You should see one error about there not being a git tag, and that's fine.
 To actually release, run:
 
 ```bash
-# use `git tag -l | grep cli` to find the latest version and what you want to bump it to
-export VERSION=0.1.1
-git tag -a v$VERSION -m "Bugfixes"
-git push origin v$VERSION
-make release
+# use `git describe --abbrev=0` to find the latest version and then bump it following https://semver.org/
+./scripts/release.sh <version> [description]
 ```

cmd/browsers.go

@@ -219,10 +219,13 @@ func (b BrowsersCmd) List(ctx context.Context, in BrowsersListInput) error {
 		return util.CleanedUpSdkError{Err: err}
 	}
 
-	browsers := page.Items
+	var browsers []kernel.BrowserListResponse
+	if page != nil {
+		browsers = page.Items
+	}
 
 	if in.Output == "json" {
-		if browsers == nil {
+		if len(browsers) == 0 {
 			fmt.Println("[]")
 			return nil
 		}

cmd/browsers_test.go

@@ -120,6 +120,21 @@ func TestBrowsersList_PrintsEmptyMessage(t *testing.T) {
 	assert.Contains(t, out, "No running browsers found")
 }
 
+func TestBrowsersList_PrintsEmptyMessagePageIsNil(t *testing.T) {
+	setupStdoutCapture(t)
+
+	fake := &FakeBrowsersService{
+		ListFunc: func(ctx context.Context, query kernel.BrowserListParams, opts ...option.RequestOption) (*pagination.OffsetPagination[kernel.BrowserListResponse], error) {
+			return nil, nil
+		},
+	}
+	b := BrowsersCmd{browsers: fake}
+	_ = b.List(context.Background(), BrowsersListInput{})
+
+	out := outBuf.String()
+	assert.Contains(t, out, "No running browsers found")
+}
+
 func TestBrowsersList_PrintsTableWithRows(t *testing.T) {
 	setupStdoutCapture(t)
 

scripts/release.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -e
+
+if [ -z "$1" ]; then
+    echo "Error: VERSION is required"
+    echo "Usage: $0 <VERSION> [DESCRIPTION]"
+    exit 1
+fi
+
+VERSION=$1
+if [[ ! "$VERSION" =~ ^[0-9.]+$ ]]; then
+    echo "Error: VERSION must contain only numbers and periods"
+    echo "Usage: $0 <VERSION> [DESCRIPTION]"
+    exit 1
+fi
+DESCRIPTION=${2:-"Version $VERSION"}
+
+git tag -a v$VERSION -m "$DESCRIPTION"
+git push origin v$VERSION
+make release