feat: add manual interval creation and inline entry editing

- Service: CreateInterval() validates same-day, end>start, day not closed
- Service: Update() now rejects edits on closed-day entries (ErrDayAlreadyClosed)
- Handler: POST /api/entries creates a completed interval with explicit times
- API client: entries.createInterval(startMs, endMs, note)
- Utils: parseTimeInput / toTimeInput helpers for HH:MM <-> unix ms
- Today page: '+ Add interval' form (time pickers + optional note)
- Today page: pencil button on each entry opens inline edit row (start/end/note)
- Tests: TestCreateInterval, TestCreateIntervalEndBeforeStart,
         TestCreateIntervalCrossesMidnight, TestUpdateRejectsClosedDay

internal/handler/entry_handler.go

@@ -19,12 +19,47 @@ func NewEntryHandler(svc *service.EntryService) *EntryHandler {
 
 func (h *EntryHandler) Routes(r chi.Router) {
 	r.Post("/entries/start", h.Start)
+	r.Post("/entries", h.CreateInterval)
 	r.Post("/entries/{id}/stop", h.StopByID)
 	r.Get("/entries", h.List)
 	r.Put("/entries/{id}", h.Update)
 	r.Delete("/entries/{id}", h.Delete)
 }
 
+// CreateInterval POST /api/entries  — create a completed interval with explicit times
+func (h *EntryHandler) CreateInterval(w http.ResponseWriter, r *http.Request) {
+	var body struct {
+		StartTime int64  `json:"start_time"`
+		EndTime   int64  `json:"end_time"`
+		Note      string `json:"note"`
+	}
+	if err := decodeJSON(r, &body); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid JSON")
+		return
+	}
+	if body.StartTime == 0 || body.EndTime == 0 {
+		writeError(w, http.StatusBadRequest, "start_time and end_time are required")
+		return
+	}
+	entry, err := h.svc.CreateInterval(r.Context(), service.CreateIntervalInput{
+		StartTime: body.StartTime,
+		EndTime:   body.EndTime,
+		Note:      body.Note,
+	})
+	if err != nil {
+		switch {
+		case errors.Is(err, service.ErrCrossesMidnight):
+			writeError(w, http.StatusUnprocessableEntity, err.Error())
+		case errors.Is(err, service.ErrDayAlreadyClosed):
+			writeError(w, http.StatusConflict, err.Error())
+		default:
+			writeError(w, http.StatusInternalServerError, err.Error())
+		}
+		return
+	}
+	writeJSON(w, http.StatusCreated, entry)
+}
+
 // Start POST /api/entries/start
 func (h *EntryHandler) Start(w http.ResponseWriter, r *http.Request) {
 	var body struct {