Phase 6b/7b: dashboard codes editor, decode events, human-readable briefs (AUD-115)

- New /codes dashboard page (behind the session login, linked in the top bar):
  lists every mapping by kind with Add, inline Edit+Save and Delete. Sam can put
  real teacher surnames in without a rebuild (FR-17).
- Decode timetable EVENTS through the same map as periods, so an ensemble reads
  'JAZZ ENSEMBLE - Ensemble Room - Mr KWO' instead of raw codes.
- teacherName splits comma- or space-separated codes ('HHL, OFG').
- SeedCodes is a one-time bootstrap while the table is empty, so a correction or
  a delete is never overwritten or restored.
- Tests: decode Label/Event, the /codes page (save, refuse, csrf, delete, auth),
  store re-seed behaviour. go test ./internal/... passes.

internal/web/server.go

@@ -79,6 +79,9 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /items/{id}", s.requireAuth(s.handleItemDetail))
 	mux.HandleFunc("POST /items/{id}/delete", s.requireAuth(s.handleItemDelete))
 	mux.HandleFunc("POST /items/{id}/calendar", s.requireAuth(s.handleItemCalendarPush))
+	mux.HandleFunc("GET /codes", s.requireAuth(s.handleCodesPage))
+	mux.HandleFunc("POST /codes", s.requireAuth(s.handleCodeSave))
+	mux.HandleFunc("POST /codes/delete", s.requireAuth(s.handleCodeDelete))
 	mux.HandleFunc("POST /summaries/build", s.requireAuth(s.handleSummaryBuild))
 	mux.HandleFunc("POST /summaries/send", s.requireAuth(s.handleSendBrief))
 	mux.HandleFunc("POST /summaries/{id}/send", s.requireAuth(s.handleSummarySend))
@@ -1421,6 +1424,139 @@ func pathID(r *http.Request, name string) (int64, bool) {
 	return v, true
 }
 
+// ---------- codes (the editable decode map, FR-17) ----------
+
+// codeKinds is the page order and the plain-English label for the four decode
+// groups.
+var codeKinds = []struct {
+	Kind  string
+	Label string
+	Hint  string
+}{
+	{store.CodeSubject, "Subjects", "e.g. 7SCF → Year 7 Science. New subject codes appear each term."},
+	{store.CodeTeacher, "Teachers", "Compass gives initials only. Put the surname here, e.g. KNI → Mr Knight. Unknown initials stay raw."},
+	{store.CodeRoom, "Rooms", "e.g. B11 → Room B11, GYM4 → Gym 4."},
+	{store.CodePeriod, "Period labels", "Word slots only, e.g. C → Connect. A number is always “Period N”."},
+}
+
+// codesData renders the editable decode map (AGENTS.md §4 FR-17). The map is
+// data, not code: a correction here changes the very next brief.
+type codesData struct {
+	Title      string
+	Username   string
+	CSRF       string
+	Version    string
+	AppEnv     string
+	Groups     []codeGroup
+	ErrMsg     string
+	Flash      string
+	FlashLevel string
+}
+
+type codeGroup struct {
+	Kind  string
+	Label string
+	Hint  string
+	Codes []codeRow
+}
+
+type codeRow struct {
+	Kind string
+	Code string
+	Name string
+}
+
+// handleCodesPage lists every mapping so Sam can correct it in the dashboard.
+func (s *Server) handleCodesPage(w http.ResponseWriter, r *http.Request) {
+	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
+	defer cancel()
+
+	data := codesData{
+		Title:    "Codes",
+		Username: s.cfg.AdminUsername,
+		CSRF:     s.auth.EnsureCSRF(w, r),
+		Version:  s.cfg.Version,
+		AppEnv:   s.cfg.AppEnv,
+	}
+	// Same flash contract as the dashboard: ?msg=… is the text, ?level=error
+	// makes it red.
+	if msg := strings.TrimSpace(r.URL.Query().Get("msg")); msg != "" {
+		data.Flash = msg
+		data.FlashLevel = "ok"
+	}
+	if strings.TrimSpace(r.URL.Query().Get("level")) == "error" {
+		data.FlashLevel = "error"
+	}
+
+	rows, err := s.store.ListCodes(ctx)
+	if err != nil {
+		s.log.Error("list codes", "err", err)
+		data.ErrMsg = "Could not read the codes: " + err.Error()
+	}
+	byKind := map[string][]codeRow{}
+	for _, c := range rows {
+		byKind[c.Kind] = append(byKind[c.Kind], codeRow{Kind: c.Kind, Code: c.Code, Name: c.Name})
+	}
+	for _, k := range codeKinds {
+		data.Groups = append(data.Groups, codeGroup{Kind: k.Kind, Label: k.Label, Hint: k.Hint, Codes: byKind[k.Kind]})
+	}
+	s.render(w, r, "codes.html", data)
+}
+
+// handleCodeSave creates or corrects one mapping (FR-17).
+func (s *Server) handleCodeSave(w http.ResponseWriter, r *http.Request) {
+	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
+	defer cancel()
+
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
+	if !s.auth.CheckCSRF(r) {
+		s.log.Warn("code save rejected: bad csrf token")
+		http.Error(w, "session expired", http.StatusForbidden)
+		return
+	}
+	row, err := s.store.SetCode(ctx,
+		strings.TrimSpace(r.PostFormValue("kind")),
+		strings.TrimSpace(r.PostFormValue("code")),
+		strings.TrimSpace(r.PostFormValue("name")))
+	if err != nil {
+		s.redirectAfterWrite(w, r, "/codes?level=error&msg="+url.QueryEscape("Not saved: "+err.Error()))
+		return
+	}
+	s.log.Info("code saved", "kind", row.Kind, "code", row.Code, "name", row.Name)
+	s.redirectAfterWrite(w, r, "/codes?msg="+url.QueryEscape("Saved "+row.Kind+" "+row.Code+" → "+row.Name))
+}
+
+// handleCodeDelete removes one mapping, so the code falls back to raw.
+func (s *Server) handleCodeDelete(w http.ResponseWriter, r *http.Request) {
+	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
+	defer cancel()
+
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
+	if !s.auth.CheckCSRF(r) {
+		s.log.Warn("code delete rejected: bad csrf token")
+		http.Error(w, "session expired", http.StatusForbidden)
+		return
+	}
+	kind := strings.TrimSpace(r.PostFormValue("kind"))
+	code := strings.TrimSpace(r.PostFormValue("code"))
+	ok, err := s.store.DeleteCode(ctx, kind, code)
+	switch {
+	case err != nil:
+		s.redirectAfterWrite(w, r, "/codes?level=error&msg="+url.QueryEscape("Not removed: "+err.Error()))
+	case !ok:
+		s.redirectAfterWrite(w, r, "/codes?level=error&msg="+url.QueryEscape("No such code: "+kind+" "+code))
+	default:
+		s.log.Info("code deleted", "kind", kind, "code", code)
+		s.redirectAfterWrite(w, r, "/codes?msg="+url.QueryEscape("Removed "+kind+" "+code+"; it renders raw again."))
+	}
+}
+
 // ---------- partials ----------
 
 func (s *Server) handleScanStatusPartial(w http.ResponseWriter, r *http.Request) {