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/tests/client/settings-render-keys-migration.svelte.test.ts

@@ -0,0 +1,64 @@
+// Guards the unfolding of `renderContentAsRawText` back onto the two
+// per-surface render keys. The single toggle carried user content and
+// thinking at once, so only the user key is restored from it and thinking
+// returns to its own default. The toggle is removed from the persisted
+// config so it does not stay orphaned in localStorage.
+
+import { CONFIG_LOCALSTORAGE_KEY } from '$lib/constants/storage';
+import { MigrationService } from '$lib/services/migration.service';
+import { config, settingsStore } from '$lib/stores/settings.svelte';
+import { beforeEach, describe, expect, it } from 'vitest';
+
+const RENDER_KEYS_MIGRATION_ID = 'render-keys-unfold-v1';
+
+async function seedConfig(stored: Record<string, unknown>) {
+	localStorage.setItem(CONFIG_LOCALSTORAGE_KEY, JSON.stringify(stored));
+
+	const migration = MigrationService.getMigrations().find((m) => m.id === RENDER_KEYS_MIGRATION_ID);
+
+	await migration?.run();
+	settingsStore.initialize();
+}
+
+function persisted(): Record<string, unknown> {
+	return JSON.parse(localStorage.getItem(CONFIG_LOCALSTORAGE_KEY) ?? '{}');
+}
+
+describe('renderContentAsRawText unfolding', () => {
+	beforeEach(() => {
+		localStorage.removeItem(CONFIG_LOCALSTORAGE_KEY);
+		MigrationService.resetState();
+		settingsStore.initialize();
+	});
+
+	it('maps raw text to user content as plain text', async () => {
+		await seedConfig({ renderContentAsRawText: true });
+		expect(config().renderUserContentAsMarkdown).toBe(false);
+	});
+
+	it('maps markdown to user content as markdown', async () => {
+		await seedConfig({ renderContentAsRawText: false });
+		expect(config().renderUserContentAsMarkdown).toBe(true);
+	});
+
+	it('leaves thinking on its own default', async () => {
+		await seedConfig({ renderContentAsRawText: true });
+		expect(config().renderThinkingAsMarkdown).toBe(true);
+	});
+
+	it('keeps an explicit user preference over the toggle', async () => {
+		await seedConfig({ renderContentAsRawText: true, renderUserContentAsMarkdown: true });
+		expect(config().renderUserContentAsMarkdown).toBe(true);
+	});
+
+	it('drops the toggle from the persisted config', async () => {
+		await seedConfig({ renderContentAsRawText: true });
+		expect(persisted().renderContentAsRawText).toBeUndefined();
+	});
+
+	it('leaves both surfaces on markdown when nothing is stored', async () => {
+		await seedConfig({});
+		expect(config().renderUserContentAsMarkdown).toBe(true);
+		expect(config().renderThinkingAsMarkdown).toBe(true);
+	});
+});