Phase 5: reply drafts — template/LLM draft, edit, SMTP send (AUD-71)

Implements Phase 5 of AGENTS.md §11 (FR-8, FR-15):

- Message detail pane (GET /partials/message) with body, recommended
  action, reply identity, template picker, editable draft, and history.
- internal/reply: OmniRoute (OpenAI-compatible) chat client and a
  template-based draft generator. All non-JEV models go through
  OmniRoute (§10).
- internal/mailops: SMTP send over smtp.gmail.com:587 with STARTTLS and
  the app password, forcing IPv4 (§9); FR-15 reply identity (send as the
  arrived-at X-Pm-Original-To address, else "Sam Rolfe"); threading via
  In-Reply-To/References; -check-smtp safe verification; and a
  [Gmail]/Sent Mail thread check.
- Migration v5 stores messages.message_id_header and drafts.sent_at;
  mailfetch parses Message-ID.
- Send is user-triggered only: CSRF + UI confirm + confirm=yes guard,
  no auto-send, duplicate-send refused. A sent reply files the original
  under Replied-to/<address> and logs every step (FR-13).
- Tests for reply, mailops SMTP/identity/thread check, store drafts and
  migration v5, and the server draft/edit/send guards.
- docs/phase5-replies.md, README, .env.example, docker-compose updated.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

web/templates/inbox.html

@@ -62,7 +62,8 @@
         <input class="msg-select" type="checkbox" name="ids" value="{{.ID}}" aria-label="Select message from {{.From}}">
         <div class="msg-main">
           <div class="msg-from">{{.From}}</div>
-          <div class="msg-subject">{{.Subject}}</div>
+          <button type="button" class="msg-subject msg-open"
+                  hx-get="/partials/message?id={{.ID}}" hx-target="#message-detail" hx-swap="innerHTML">{{.Subject}}</button>
           {{if .SourceAddr}}<div class="msg-source">arrived at <span class="source-addr">{{.SourceAddr}}</span></div>{{end}}
         </div>
         <div class="msg-meta">