chore: merge main, resolve biome formatting conflicts

Merge origin/main into feat/external-2fa-codes. Resolve formatting
conflicts caused by biome rollout; preserve both feature streams:
PR's external 2FA token + signing-session 2FA proof additions plus
main's RateLimit/RecipientExpired/signingReminders/date-auto-insert.

In complete-document-with-token.ts, drop the duplicate early
field-fetching block introduced when main moved that logic later
with date auto-insert support; keep the EXTERNAL_TWO_FACTOR_AUTH
check using derivedRecipientActionAuth.

apps/docs/source.config.ts

@@ -0,0 +1,23 @@
+import { remarkMdxMermaid } from 'fumadocs-core/mdx-plugins';
+import { defineConfig, defineDocs, frontmatterSchema, metaSchema } from 'fumadocs-mdx/config';
+
+// You can customise Zod schemas for frontmatter and `meta.json` here
+// see https://fumadocs.dev/docs/mdx/collections
+export const docs = defineDocs({
+  dir: 'content/docs',
+  docs: {
+    schema: frontmatterSchema,
+    postprocess: {
+      includeProcessedMarkdown: true,
+    },
+  },
+  meta: {
+    schema: metaSchema,
+  },
+});
+
+export default defineConfig({
+  mdxOptions: {
+    remarkPlugins: [remarkMdxMermaid],
+  },
+});