Add submissions form

Authors can now send a manuscript, headshot, bio, and pitch through a
real form instead of "Coming soon." Posts multipart to eec's new
/submissions endpoint (self-hosted, keeps the privacy policy's existing
no-third-party-SaaS promise true). Also documents the new data
collection in the privacy policy.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

content/privacy.md

@@ -11,6 +11,9 @@ use of twosquirrelspress.com, and what happens to it.
 ## What Two Squirrels Press collects
 
 - Your name, email address, and message, when you submit the contact form.
+- Your name, email address, manuscript file, author bio, a description of
+  your submission, the title or call it's for, and a headshot if you
+  provide one, when you submit the submissions form.
 
 That's it — this site doesn't run a newsletter, doesn't sell anything
 directly, and doesn't use third-party analytics, ad trackers, or tracking
@@ -19,6 +22,7 @@ pixels.
 ## Why Two Squirrels Press collects it
 
 - To respond to messages sent through the contact form.
+- To evaluate submissions sent through the submissions form.
 
 ## What Two Squirrels Press doesn't do