Phase 2: Gmail IMAP fetch (IPv4), FR-2 source address, real mail in dashboard (AUD-67)

- internal/mailfetch: stdlib-only read-only IMAP client (LOGIN, SELECT,
  UID SEARCH, UID FETCH) that always dials tcp4; IPv6 to Gmail is broken
  from .13 and caused a socket EOF.
- MIME parsing to text, RFC2047 header decoding, FR-2 source address:
  X-Pm-Original-To -> To -> Received 'for <addr>' -> Return-Path, never
  Delivered-To. The matched header is recorded for audit.
- store: Message upsert/list/count + LogAction; schema migration v2 adds
  imap_uid and imap_uidvalidity.
- server: dashboard and /partials/inbox render real mail grouped by
  category with a recommended action; POST /actions/fetch runs a scan
  (CSRF-checked); nav counts; 'Check mail' button.
- config: GMAIL_USER, GMAIL_APP_PASSWORD, IMAP host/port/lookback/max.
- cmd: -fetch runs one scan and exits (n8n/CLI entry point, FR-1).
- compose/.env.example expose the Gmail + IMAP settings.
- tests: FR-2 precedence, MIME bodies, IMAP literal/parser, store
  upsert/migration, inbox rendering.

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

web/templates/dashboard.html

@@ -46,11 +46,16 @@
           <div class="nav-group">
             <div class="nav-group-title">Categories</div>
             <div class="nav-group-items">
+              <a class="nav-item nav-item-active" href="#">
+                <span class="dot" style="background: var(--primary)"></span>
+                <span>All mail</span>
+                <span class="count">{{.Total}}</span>
+              </a>
               {{range .Categories}}
               <a class="nav-item" href="#">
                 <span class="dot" style="background: {{.Color}}"></span>
                 <span>{{.Name}}</span>
-                <span class="count">0</span>
+                <span class="count">{{.Count}}</span>
               </a>
               {{end}}
             </div>
@@ -73,10 +78,17 @@
       <section class="panel" aria-label="Message list">
         <div class="panel-head">
           <h2>Inbox</h2>
-          <button class="btn btn-utility" type="button"
-                  hx-get="/partials/inbox" hx-target="#inbox-list" hx-swap="innerHTML">
-            Refresh
-          </button>
+          <div class="panel-actions">
+            <button class="btn btn-primary" type="button"
+                    hx-post="/actions/fetch" hx-target="#inbox-list" hx-swap="innerHTML"
+                    hx-headers='{"X-CSRF-Token": "{{.CSRFToken}}"}'>
+              Check mail
+            </button>
+            <button class="btn btn-utility" type="button"
+                    hx-get="/partials/inbox" hx-target="#inbox-list" hx-swap="innerHTML">
+              Refresh
+            </button>
+          </div>
         </div>
         <div id="inbox-list" class="msg-list"
              hx-get="/partials/inbox" hx-trigger="load" hx-swap="innerHTML"></div>