fix: exclude source maps from the npm package (#3295)

Stacked on #3293.

#1948 enabled source maps for local debugging and added `!*.js.map` to
`files` in `package.json` to keep them out of the npm package. npm
matches a negated `files` entry only at the package root, so the entry
never matched the source maps in `build/src`, and the package has
included them since then. This PR changes the entry to `!**/*.js.map`,
the same form that #3293 uses for `.d.ts` files.

The published maps were of little use: they do not embed
`sourcesContent`, and the TypeScript sources that they reference are not
in the package.

## User-visible changes

- The npm package no longer includes `.js.map` files (100 files in a
local `npm pack --dry-run`).
- The published `.js` files still end with `//# sourceMappingURL=`
comments, which now point to files that are not in the package. Tools
that load source maps, such as debuggers, can warn that the map is
missing.

## Testing

- `npm pack --dry-run` lists no `.js.map` files and still lists the
`.js` files.
- `npm run format`
- `npm run test`

package.json

@@ -43,7 +43,7 @@
     "LICENSE",
     "skills",
     "!*.tsbuildinfo",
-    "!*.js.map",
+    "!**/*.js.map",
     "!**/*.d.ts"
   ],
   "repository": "ChromeDevTools/chrome-devtools-mcp",