docs: sync plugin card descriptions with package.json

The plugins reference page's `LinkCard` descriptions predate the July
pass that normalized every plugin's npm `description` to imperative
mood, so after #3019 (which correctly reused the current descriptions
for its three new cards) the page mixed the two voices. Sync the five
stale cards with each package's `package.json`: `markdown-shortcuts`,
`one-line`, `paste-link`, and `sdk-value` move to the imperative form,
and `typeahead-picker` picks up its rewritten description ("Build
typeahead pickers (emoji, mentions, slash commands)..."). The
`paste-link` card also gains the trailing period every other card on
the page has. The remaining four cards already matched.

Author: christianhg

apps/docs/src/content/docs/editor/reference/plugins.mdx

@@ -73,22 +73,22 @@ function LogTextPlugin() {
   />
   <LinkCard
     title="@portabletext/plugin-markdown-shortcuts"
-    description="Adds helpful Markdown shortcuts to the editor."
+    description="Add helpful Markdown shortcuts to the editor."
     href="https://github.com/portabletext/editor/tree/main/packages/plugin-markdown-shortcuts"
   />
   <LinkCard
     title="@portabletext/plugin-one-line"
-    description="Restricts the Portable Text Editor to a single line."
+    description="Restrict the Portable Text Editor to a single line."
     href="https://github.com/portabletext/editor/tree/main/packages/plugin-one-line"
   />
   <LinkCard
     title="@portabletext/plugin-paste-link"
-    description="Allows pasting links in the Portable Text Editor"
+    description="Allow pasting links in the Portable Text Editor."
     href="https://github.com/portabletext/editor/tree/main/packages/plugin-paste-link"
   />
   <LinkCard
     title="@portabletext/plugin-sdk-value"
-    description="Connects a Portable Text Editor with a Sanity document using the SDK."
+    description="Connect a Portable Text Editor with a Sanity document using the SDK."
     href="https://github.com/portabletext/editor/tree/main/packages/plugin-sdk-value"
   />
   <LinkCard
@@ -98,7 +98,7 @@ function LogTextPlugin() {
   />
   <LinkCard
     title="@portabletext/plugin-typeahead-picker"
-    description="Generic typeahead picker infrastructure for the Portable Text Editor."
+    description="Build typeahead pickers (emoji, mentions, slash commands) for the Portable Text Editor."
     href="https://github.com/portabletext/editor/tree/main/packages/plugin-typeahead-picker"
   />
   <LinkCard