ui: UI/chat form follow ups (#26743)

* ui: split the markdown rendering setting per surface

User content and thinking get their own toggle again, so turning off
markdown for a message leaves reasoning blocks formatted. Both default
to markdown. A stored renderContentAsRawText unfolds onto the user key
and is dropped from the config.

File mentions render as badges in the raw text path too, through a
narrow pass over [name](file://path) that leaves everything else
untouched.

* ui: let the rich chat input scroll past its max height

The contenteditable renderer caps its height with max-height but had no
overflow rule, so a long buffer overflowed into the input area wrapper
and got clipped by its overflow-hidden, leaving no way to reach the
bottom of the message. The textarea renderer scrolls natively and was
never affected.

* ui: apply the new lint and format config

* ui: move the render keys unfolding into the migration service

Address review from @allozaur: the settings store no longer rewrites
persisted config on load, the raw text toggle now unfolds onto the
per-surface render keys in migration.service.ts, next to the other
config migrations. The mention scanner flag and the directory path
suffix become named constants.

tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessageReasoningBlock.svelte

@@ -140,7 +140,7 @@
 		class:is-streaming={isPending}
 		onscroll={handleScrollEvent}
 	>
-		{#if !currentConfig.renderContentAsRawText}
+		{#if currentConfig.renderThinkingAsMarkdown}
 			<MarkdownContent content={section.content} class="text-muted-foreground" {attachments} />
 		{:else}
 			<div