sort: ["source-order"] should apply to group ordering, not just group members

Current Behavior

When sort: ["source-order"] is configured in typedoc.json, it only affects the ordering of items within groups, not the groups themselves. Groups are always ordered alphabetically.

Example configuration:

{
  "sort": [
    "source-order"
  ]
}

Source code order:

/**
 * @group Comparators
 */
export function ascending() { }

/**
 * @group Factories
 */
export function by() { }

/**
 * @group Combinators
 */
export function reverse() { }

Generated docs show groups in alphabetical order:

1. Combinators
2. Comparators
3. Factories

Expected Behavior

When sort: ["source-order"] is configured, groups whose order is not explicitly specified in groupOrder should be sorted by source order rather than alphabetically:

1. Comparators (first @group in source)
2. Factories (second @group in source)
3. Combinators (third @group in source)

Note: groupOrder should maintain precedence when explicitly specified. This is about the fallback behavior for unspecified groups.

Current Workaround

Must explicitly configure groupOrder:

{
  "sort": [
    "source-order"
  ],
  "groupOrder": [
    "Comparators",
    "Factories",
    "Combinators",
    "*"
  ]
}

Proposed Solution

Modify group sorting behavior to respect the sort option when groupOrder doesn't explicitly specify all groups:

• Groups listed in groupOrder maintain their explicit order (preserves existing behavior)
• Unlisted groups fall back to sort: ["source-order"] if configured, alphabetically otherwise
• Update groupOrder documentation from "Groups whose order is not specified will be sorted alphabetically" to "Groups whose order is not specified will be sorted by source order if sort: ["source-order"] is configured, alphabetically otherwise."