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>

internal/store/schema.sql

@@ -36,6 +36,19 @@ CREATE INDEX IF NOT EXISTS idx_messages_received_at ON messages (received_at);
 CREATE INDEX IF NOT EXISTS idx_messages_thread_id   ON messages (thread_id);
 CREATE INDEX IF NOT EXISTS idx_messages_source      ON messages (source_address);
 
+-- FR-14: the editable category list. `name` is the stable key stored in
+-- classifications.category and sent to JEV as the Choice option name. Renaming a
+-- category cascades to existing classifications (see store.RenameCategory).
+CREATE TABLE IF NOT EXISTS categories (
+    id          INTEGER PRIMARY KEY AUTOINCREMENT,
+    name        TEXT    NOT NULL COLLATE NOCASE UNIQUE,
+    description TEXT    NOT NULL DEFAULT '',
+    position    INTEGER NOT NULL DEFAULT 0,
+    created_at  TEXT    NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE INDEX IF NOT EXISTS idx_categories_position ON categories (position, name);
+
 -- FR-3, FR-14: classifier output per message.
 CREATE TABLE IF NOT EXISTS classifications (
     id           INTEGER PRIMARY KEY AUTOINCREMENT,