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/preflight/preflight.go

@@ -0,0 +1,160 @@
+package preflight
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"github.com/prosolis/Pastel/internal/config"
+	"github.com/prosolis/Pastel/internal/matrix"
+)
+
+type Result struct {
+	Name   string
+	Status string // "pass", "fail", "skip"
+	Detail string
+}
+
+// Run executes all preflight checks and returns results.
+func Run(cfg *config.Config) []Result {
+	var results []Result
+
+	results = append(results, checkMatrix(cfg))
+	results = append(results, checkFrankfurter())
+
+	if cfg.HasSource("cheapshark") {
+		results = append(results, checkCheapShark())
+	} else {
+		results = append(results, Result{"CheapShark", "skip", "not in DEAL_SOURCES"})
+	}
+
+	results = append(results, checkEpic())
+
+	if cfg.ITADAPIKey != "" || cfg.HasSource("itad") {
+		results = append(results, checkITAD(cfg))
+	} else {
+		results = append(results, Result{"IsThereAnyDeal", "skip", "no API key and not in DEAL_SOURCES"})
+	}
+
+	return results
+}
+
+// PrintResults prints preflight results and returns true if all passed.
+func PrintResults(results []Result) bool {
+	allPass := true
+	for _, r := range results {
+		var icon string
+		switch r.Status {
+		case "pass":
+			icon = "✓"
+		case "fail":
+			icon = "✗"
+			allPass = false
+		case "skip":
+			icon = "–"
+		}
+		fmt.Printf("  %s %s: %s\n", icon, r.Name, r.Detail)
+	}
+	return allPass
+}
+
+func checkMatrix(cfg *config.Config) Result {
+	client, err := matrix.New(cfg.MatrixHomeserverURL, cfg.MatrixBotUserID, cfg.MatrixBotAccessToken, "")
+	if err != nil {
+		return Result{"Matrix", "fail", fmt.Sprintf("client error: %v", err)}
+	}
+
+	who, err := client.Whoami()
+	if err != nil {
+		return Result{"Matrix", "fail", fmt.Sprintf("whoami failed: %v", err)}
+	}
+
+	rooms, err := client.JoinedRooms()
+	if err != nil {
+		return Result{"Matrix", "fail", fmt.Sprintf("joined_rooms failed: %v", err)}
+	}
+
+	inRoom := false
+	for _, r := range rooms {
+		if r == cfg.MatrixDealsRoomID {
+			inRoom = true
+			break
+		}
+	}
+
+	if !inRoom {
+		return Result{"Matrix", "fail", fmt.Sprintf("bot %s is not in room %s", who, cfg.MatrixDealsRoomID)}
+	}
+
+	return Result{"Matrix", "pass", fmt.Sprintf("authenticated as %s, in target room", who)}
+}
+
+func checkCheapShark() Result {
+	resp, err := http.Get("https://www.cheapshark.com/api/1.0/deals?pageSize=1")
+	if err != nil {
+		return Result{"CheapShark", "fail", fmt.Sprintf("request failed: %v", err)}
+	}
+	defer resp.Body.Close()
+
+	var deals []json.RawMessage
+	if err := json.NewDecoder(resp.Body).Decode(&deals); err != nil || len(deals) == 0 {
+		return Result{"CheapShark", "fail", "unexpected response format"}
+	}
+
+	return Result{"CheapShark", "pass", "API reachable"}
+}
+
+func checkEpic() Result {
+	resp, err := http.Get("https://store-site-backend-static.ak.epicgames.com/freeGamesPromotions?locale=en-US")
+	if err != nil {
+		return Result{"Epic Games", "fail", fmt.Sprintf("request failed: %v", err)}
+	}
+	defer resp.Body.Close()
+
+	var result struct {
+		Data struct {
+			Catalog struct {
+				SearchStore struct {
+					Elements []json.RawMessage `json:"elements"`
+				} `json:"searchStore"`
+			} `json:"Catalog"`
+		} `json:"data"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return Result{"Epic Games", "fail", "unexpected response format"}
+	}
+
+	return Result{"Epic Games", "pass", fmt.Sprintf("API reachable, %d elements", len(result.Data.Catalog.SearchStore.Elements))}
+}
+
+func checkFrankfurter() Result {
+	resp, err := http.Get("https://api.frankfurter.dev/v1/latest?base=USD&symbols=CAD,EUR,GBP")
+	if err != nil {
+		return Result{"Frankfurter", "fail", fmt.Sprintf("request failed: %v", err)}
+	}
+	defer resp.Body.Close()
+
+	var result struct {
+		Rates map[string]float64 `json:"rates"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil || len(result.Rates) == 0 {
+		return Result{"Frankfurter", "fail", "no rates returned"}
+	}
+
+	return Result{"Frankfurter", "pass", fmt.Sprintf("rates: %v", result.Rates)}
+}
+
+func checkITAD(cfg *config.Config) Result {
+	url := fmt.Sprintf("https://api.isthereanydeal.com/games/lookup/v1?key=%s&appid=220", cfg.ITADAPIKey)
+	resp, err := http.Get(url)
+	if err != nil {
+		return Result{"IsThereAnyDeal", "fail", fmt.Sprintf("request failed: %v", err)}
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == 401 || resp.StatusCode == 403 {
+		return Result{"IsThereAnyDeal", "fail", "invalid API key"}
+	}
+
+	return Result{"IsThereAnyDeal", "pass", "API key valid"}
+}