Add add-on management: registry browser, install, remove (step 5)

Browse the ~270-entry DDEV add-on registry with search, install via
`ddev addon get`, remove via `ddev addon remove` — both routed through
the streaming commandRunner. `addon get`/`remove` support `--project
<name>` directly (unlike snapshot restore), so no cwd trick needed
here. Verified working with the project stopped, per the plan's
requirement.

Found and fixed a real bug via live UI testing: `ddev addon list
--installed --json-output` omits the `raw` key entirely when nothing
is installed (unlike `ddev list`/`ddev snapshot --list`, which include
`raw: null`). The shared runDdevRead helper treated that as an error,
so after removing the last add-on the query errored on refetch and
React Query kept showing the stale cached row instead of clearing it.
Split the helper into runDdevRead (strict, for describeProject where
missing data is a real error) and runDdevReadList (treats missing raw
as empty, for every list-style command) and fixed all four list call
sites to use it.

Verified end-to-end via CDP-driven clicks against the real scratch
project: search filtering, install (streamed output, confirmed via
`ddev addon list --installed` on the CLI), and remove — including
re-confirming after the fix that the installed-add-ons table actually
clears instead of showing stale data.

src/main/index.ts

@@ -5,6 +5,7 @@ import icon from '../../resources/icon.png?asset'
 import { registerProjectsIpc } from './ipc/projects'
 import { registerTerminalIpc } from './ipc/terminal'
 import { registerDatabaseIpc } from './ipc/database'
+import { registerAddonsIpc } from './ipc/addons'
 
 function createWindow(): void {
   // Create the browser window.
@@ -56,6 +57,7 @@ app.whenReady().then(() => {
   registerProjectsIpc()
   registerTerminalIpc()
   registerDatabaseIpc()
+  registerAddonsIpc()
 
   createWindow()