chore(gitignore): untrack inspect dist/index.html build artifact

index.html is regenerated by vite on every build with a new content hash,
making it permanently dirty. Only .gitkeep is needed for //go:embed to
compile on a fresh checkout. Also remove duplicate dist/* line and stale
d2 diagram ignore entries.

internal/inspect/dist/index.html

@@ -1,13 +0,0 @@
-<!doctype html>
-<html lang="en">
-  <head>
-    <meta charset="UTF-8" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <title>sanderling inspect</title>
-    <script type="module" crossorigin src="/assets/index-DFpYQDqN.js"></script>
-    <link rel="stylesheet" crossorigin href="/assets/index-BSJUf7yI.css">
-  </head>
-  <body>
-    <div id="root"></div>
-  </body>
-</html>