AI Reply menu: '...' kebab opens a note input to steer the draft

The Fast/Full popover now has a kebab (three-dot) button alongside the
two preset choices. Clicking it expands a textarea below with a
'Draft with note' send button. The textarea is for the user to tell
the AI how to reply ('confirm Tuesday at 2', 'decline politely', 'say
we'll need an extra week') instead of accepting a generic draft.

Plumbing:
- emailLibrary.js: kebab button + note panel inside .email-ai-reply-choice
  menu. Submitting calls _runAiReplyFromButton with mode='ai-reply-full'
  and a noteHint string.
- _runAiReplyFromButton signature gains noteHint; passes it through
  state._onEmailClick as opts.noteHint.
- emailInbox.js consumer: forwards opts.noteHint into _openEmail's new
  5th arg, which puts it in the /api/email/ai-reply POST body as
  user_hint.
- routes/email_routes.py /ai-reply: reads user_hint, appends a
  'User's instructions for THIS reply' section to the user message
  (priority over default tone/length). Also skips the per-message
  AI-reply cache when a hint is set — the cached generic draft would
  silently override the instructions otherwise.

static/js/emailInbox.js

@@ -118,7 +118,7 @@ export function init(documentModule) {
       } catch (_) {}
       if (opts.compose) { _composeNew(); return; }
       if (opts.email) {
-        await _openEmail(opts.email, null, opts.emailData, opts.mode || 'reply');
+        await _openEmail(opts.email, null, opts.emailData, opts.mode || 'reply', opts.noteHint || '');
       }
     },
   });
@@ -630,7 +630,7 @@ function _createEmailItem(em) {
   return item;
 }
 
-async function _openEmail(em, itemEl, preloadedData = null, mode = 'reply') {
+async function _openEmail(em, itemEl, preloadedData = null, mode = 'reply', noteHint = '') {
   const aiReplyMode = mode === 'ai-reply-fast' ? 'fast' : (mode === 'ai-reply-full' ? 'full' : '');
   const wantsAiReply = mode === 'ai-reply' || !!aiReplyMode;
   let aiSuggestedBody = null;
@@ -690,6 +690,7 @@ async function _openEmail(em, itemEl, preloadedData = null, mode = 'reply') {
               uid: String(em.uid || ''),
               folder: _currentFolder,
               fast: aiReplyMode ? aiReplyMode === 'fast' : _shouldUseFastAiReply(data),
+              user_hint: (noteHint || '').trim() || undefined,
             }),
           });
           const result = await res.json();