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>

internal/store/schema.sql

@@ -18,6 +18,9 @@ CREATE TABLE IF NOT EXISTS messages (
     id              INTEGER PRIMARY KEY AUTOINCREMENT,
     gmail_id        TEXT    NOT NULL UNIQUE,
     thread_id       TEXT,
+    -- Phase 5 (FR-8): the RFC822 Message-ID header. A reply sets In-Reply-To and
+    -- References to it so Gmail files the reply in the same thread.
+    message_id_header TEXT,
     from_addr       TEXT,
     to_addr         TEXT,
     subject         TEXT,
@@ -105,7 +108,9 @@ CREATE TABLE IF NOT EXISTS drafts (
     message_id   INTEGER NOT NULL REFERENCES messages (id) ON DELETE CASCADE,
     body         TEXT    NOT NULL,
     template_id  TEXT,
+    -- Phase 5 (FR-8): draft -> sent. sent_at is set when the SMTP send succeeds.
     status       TEXT    NOT NULL DEFAULT 'draft',
+    sent_at      TEXT,
     created_at   TEXT    NOT NULL DEFAULT (datetime('now')),
     updated_at   TEXT    NOT NULL DEFAULT (datetime('now'))
 );