Phase 3: JEV classification, rules table, editable categories (AUD-69)

Implements FR-3, FR-4, FR-5 and FR-14.

- internal/classify: TypeSafe System One (JEV) HTTP client with the confirmed
  request/response shape, retry with backoff on 429/529/5xx, a plain-text rule
  engine (first match wins, overrides only the named fields), and bounded
  orchestration with a per-run cap.
- internal/store: migration v3 adds an editable `categories` table (name =
  JEV Choice option and classifications key; rename cascades, remove reassigns)
  and seeds a starter rules version once. Classification persistence, coverage,
  and pending/all message queries.
- internal/server: POST /actions/classify and /actions/reclassify, plus the
  FR-14 category editor (GET /categories and add/rename/remove). The triage list
  now groups by the live category list and shows action + confidence.
- CLI: -classify and -classify-all for n8n.
- Docs: docs/phase3-classify.md with the confirmed JEV shape, a live read-only
  classification, and the DoD evidence.

DoD: all 100 stored messages have a non-null category, importance, and suggested
action (0 nulls); JEV picked a newly added/renamed category for 6 real messages
over HTTP. One live JEV call recorded in the phase doc.

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

web/templates/inbox.html

@@ -18,6 +18,7 @@
       </div>
       <div class="msg-meta">
         <span class="pill action-pill">{{.Action}}</span>
+        {{if .Classified}}<span class="msg-confidence" title="Classifier confidence">{{.Confidence}}%</span>{{end}}
         {{if .When}}<span class="msg-when">{{.When}}</span>{{end}}
       </div>
     </div>
@@ -27,7 +28,7 @@
 {{else}}
 <div class="empty-state">
   <div class="empty-title">No messages yet</div>
-  <p class="empty-copy">Use <strong>Check mail</strong> to fetch from Gmail. New messages appear here, grouped by category, with a recommended action on each row.</p>
+  <p class="empty-copy">Use <strong>Check mail</strong> to fetch from Gmail, then <strong>Classify</strong> to let JEV sort each message.</p>
   <span class="pill">No stored messages</span>
 </div>
 {{end}}