Rewrite Pastel from Python to Go with watchlist feature

Full rewrite of the gaming deals Matrix bot in Go for better performance
and a single static binary. Includes all original functionality (CheapShark,
ITAD, Epic free games, multi-currency pricing, dedup, preflight checks,
presence heartbeat) plus a new watchlist feature where users can DM the bot
to watch for specific game deals with 180-day auto-expiry.

New: systemd service file, DB migration script for Python-to-Go transition.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/deals/epic.go

@@ -0,0 +1,147 @@
+package deals
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+type EpicFreeGame struct {
+	ID       string
+	Title    string
+	Desc     string
+	URL      string
+	EndDate  *time.Time
+	Upcoming bool
+	DedupID  string
+}
+
+type epicResponse struct {
+	Data struct {
+		Catalog struct {
+			SearchStore struct {
+				Elements []epicElement `json:"elements"`
+			} `json:"searchStore"`
+		} `json:"Catalog"`
+	} `json:"data"`
+}
+
+type epicElement struct {
+	ID          string `json:"id"`
+	Title       string `json:"title"`
+	Description string `json:"description"`
+	ProductSlug string `json:"productSlug"`
+	URLSlug     string `json:"urlSlug"`
+	CatalogNs   struct {
+		Mappings []struct {
+			PageSlug string `json:"pageSlug"`
+		} `json:"mappings"`
+	} `json:"catalogNs"`
+	Promotions *struct {
+		PromotionalOffers         []epicOfferGroup `json:"promotionalOffers"`
+		UpcomingPromotionalOffers []epicOfferGroup `json:"upcomingPromotionalOffers"`
+	} `json:"promotions"`
+}
+
+type epicOfferGroup struct {
+	PromotionalOffers []epicOffer `json:"promotionalOffers"`
+}
+
+type epicOffer struct {
+	StartDate       string `json:"startDate"`
+	EndDate         string `json:"endDate"`
+	DiscountSetting struct {
+		DiscountPercentage int `json:"discountPercentage"`
+	} `json:"discountSetting"`
+}
+
+// FetchEpicFreeGames fetches current and upcoming free games from Epic Games Store.
+func FetchEpicFreeGames() ([]EpicFreeGame, error) {
+	resp, err := http.Get("https://store-site-backend-static.ak.epicgames.com/freeGamesPromotions?locale=en-US")
+	if err != nil {
+		return nil, fmt.Errorf("epic request failed: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("epic returned status %d", resp.StatusCode)
+	}
+
+	var result epicResponse
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return nil, fmt.Errorf("epic decode failed: %w", err)
+	}
+
+	now := time.Now()
+	var games []EpicFreeGame
+
+	for _, elem := range result.Data.Catalog.SearchStore.Elements {
+		if elem.Promotions == nil {
+			continue
+		}
+
+		slug := elem.ProductSlug
+		if slug == "" {
+			slug = elem.URLSlug
+		}
+		if slug == "" && len(elem.CatalogNs.Mappings) > 0 {
+			slug = elem.CatalogNs.Mappings[0].PageSlug
+		}
+		storeURL := fmt.Sprintf("https://store.epicgames.com/en-US/p/%s", slug)
+
+		// Check current free offers
+		for _, group := range elem.Promotions.PromotionalOffers {
+			for _, offer := range group.PromotionalOffers {
+				if offer.DiscountSetting.DiscountPercentage != 0 {
+					continue
+				}
+				start, _ := time.Parse(time.RFC3339, offer.StartDate)
+				end, _ := time.Parse(time.RFC3339, offer.EndDate)
+
+				if start.After(now) || end.Before(now) {
+					continue
+				}
+
+				game := EpicFreeGame{
+					ID:       elem.ID,
+					Title:    elem.Title,
+					Desc:     elem.Description,
+					URL:      storeURL,
+					Upcoming: false,
+					DedupID:  fmt.Sprintf("epic-%s", elem.ID),
+				}
+				if !end.IsZero() {
+					game.EndDate = &end
+				}
+				games = append(games, game)
+			}
+		}
+
+		// Check upcoming free offers
+		for _, group := range elem.Promotions.UpcomingPromotionalOffers {
+			for _, offer := range group.PromotionalOffers {
+				if offer.DiscountSetting.DiscountPercentage != 0 {
+					continue
+				}
+
+				game := EpicFreeGame{
+					ID:       elem.ID,
+					Title:    elem.Title,
+					Desc:     elem.Description,
+					URL:      storeURL,
+					Upcoming: true,
+					DedupID:  fmt.Sprintf("epic-%s", elem.ID),
+				}
+				if offer.EndDate != "" {
+					if end, err := time.Parse(time.RFC3339, offer.EndDate); err == nil {
+						game.EndDate = &end
+					}
+				}
+				games = append(games, game)
+			}
+		}
+	}
+
+	return games, nil
+}