chore(plugin-kit): 0.4.0 — the launch surface a plugin needs to publish a tile the host cannot name

`serveUi({launch})`, `PluginLaunchTarget` and `makeLaunchHandler` (#129) are new API, so this is a
minor bump rather than a patch. It also carries `SyncError.message`, without which a host refusal
reaches a plugin's own UI as the bare tag `SyncError` and nothing else.

Unblocks rom-manager, whose main is currently RED: it merged the consuming change while still
pinning `^0.2.0`, so `bun install --frozen-lockfile` there resolves a kit without these exports and
the typecheck fails on all three. Publishing this and then bumping that pin is the fix — in that
order, because the lockfile cannot resolve 0.4.0 until it exists on the registry.

Tag `plugin-kit-v0.4.0` to publish; the workflow asserts the tag matches this version.

plugin-kit/package.json

@@ -1,6 +1,6 @@
 {
 	"name": "@punktfunk/plugin-kit",
-	"version": "0.3.3",
+	"version": "0.4.0",
 	"description": "Effect-based framework for punktfunk plugins: lifecycle runtime, config/state, sync engine, UI serving, CLI scaffold, and browser helpers.",
 	"type": "module",
 	"license": "MIT OR Apache-2.0",