`@server:` completion previously matched only the resource URI,
case-sensitively, and there was no way to reach a server without typing
its full name first.
- Match the partial after the colon case-insensitively against the
resource's friendly name/title (`title || name`) as well as the URI,
ranked URI-prefix > name-prefix > URI-substring > name-substring, and
surface the name as the suggestion description.
- Before the colon, suggest configured MCP servers that expose resources
and whose name prefixes the input, prepended to the file results (never
hiding files). Selecting one expands to `@server:` and drills into the
resource list (reuses the directory `isDirectory` continuation).
Refs #5601, follows #5635.
c1eef15d4b