fix(post): link board-specific option errors to supported boards

When fortune or dice options are used on the wrong board, show which
boards support them with clickable links in the post form and reply modal.

src/components/post-options-error-message/post-options-error-message.tsx

@@ -0,0 +1,50 @@
+import { Fragment } from 'react';
+import { Link } from 'react-router-dom';
+import type { DirectoryCommunity } from '../../hooks/use-directories';
+import type { PostOptionsValidationError } from '../../lib/utils/post-options-utils';
+
+interface PostOptionsErrorMessageProps {
+  directories?: DirectoryCommunity[];
+  error: PostOptionsValidationError;
+}
+
+const EMPTY_DIRECTORIES: DirectoryCommunity[] = [];
+const DIRECTORY_TITLE_CODE_PATTERN = /^\/([^/]+)\//;
+const DIRECTORY_TITLE_LABEL_PATTERN = /^\/[^/]+\//;
+
+const getDirectoryCode = (directory: DirectoryCommunity): string | undefined => directory.directoryCode ?? directory.title?.match(DIRECTORY_TITLE_CODE_PATTERN)?.[1];
+
+const getDirectoryLabel = (code: string, directories: DirectoryCommunity[]): string => {
+  const directory = directories.find((entry) => getDirectoryCode(entry) === code);
+  return directory?.title?.match(DIRECTORY_TITLE_LABEL_PATTERN)?.[0] ?? `/${code}/`;
+};
+
+const DirectoryLinks = ({ codes, directories }: { codes: string[]; directories: DirectoryCommunity[] }) => (
+  <>
+    {codes.map((code, index) => {
+      const separator = index === 0 ? '' : ', ';
+      return (
+        <Fragment key={code}>
+          {separator}
+          <Link to={`/${code}`}>{getDirectoryLabel(code, directories)}</Link>
+        </Fragment>
+      );
+    })}
+  </>
+);
+
+const PostOptionsErrorMessage = ({ directories = EMPTY_DIRECTORIES, error }: PostOptionsErrorMessageProps) => {
+  return (
+    <>
+      Unsupported options: {error.unsupportedOptions.join(', ')}.
+      {error.supportedDirectoryCodesByOption.map(({ option, directoryCodes }) => (
+        <Fragment key={option}>
+          {' '}
+          Option "{option}" is supported on: <DirectoryLinks codes={directoryCodes} directories={directories} />.
+        </Fragment>
+      ))}
+    </>
+  );
+};
+
+export default PostOptionsErrorMessage;