Add Steam integration showing online status and recent games

Fetches player summary and recently played games from Steam API with
5-minute server-side caching. Displays in the home sidebar with online
indicator and game artwork.

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

backend/services/steam.go

@@ -0,0 +1,83 @@
+package services
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+type SteamRecentGame struct {
+	AppID           int    `json:"appid"`
+	Name            string `json:"name"`
+	Playtime2Weeks  int    `json:"playtime_2weeks"`
+	PlaytimeForever int    `json:"playtime_forever"`
+}
+
+type SteamRecentGamesResponse struct {
+	Response struct {
+		TotalCount int               `json:"total_count"`
+		Games      []SteamRecentGame `json:"games"`
+	} `json:"response"`
+}
+
+type SteamPlayerSummary struct {
+	PersonaState int `json:"personastate"`
+}
+
+type SteamPlayerSummariesResponse struct {
+	Response struct {
+		Players []SteamPlayerSummary `json:"players"`
+	} `json:"response"`
+}
+
+func FetchRecentlyPlayedGames(apiKey, steamID string) ([]SteamRecentGame, error) {
+	url := fmt.Sprintf("https://api.steampowered.com/IPlayerService/GetRecentlyPlayedGames/v1/?key=%s&steamid=%s&count=3", apiKey, steamID)
+
+	client := &http.Client{Timeout: 5 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var result SteamRecentGamesResponse
+	if err := json.Unmarshal(body, &result); err != nil {
+		return nil, err
+	}
+
+	return result.Response.Games, nil
+}
+
+func FetchPlayerSummary(apiKey, steamID string) (*SteamPlayerSummary, error) {
+	url := fmt.Sprintf("https://api.steampowered.com/ISteamUser/GetPlayerSummaries/v2/?key=%s&steamids=%s", apiKey, steamID)
+
+	client := &http.Client{Timeout: 5 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var result SteamPlayerSummariesResponse
+	if err := json.Unmarshal(body, &result); err != nil {
+		return nil, err
+	}
+
+	if len(result.Response.Players) == 0 {
+		return nil, nil
+	}
+
+	return &result.Response.Players[0], nil
+}