Phase 4: Extract magic numbers to constants

Create config/constants.go with centralized configuration values:
- Concurrency limits (MaxConcurrentTrelloRequests)
- Timeouts (HTTP, Google Calendar, graceful shutdown, request)
- Meal times (breakfast, lunch, dinner hours)
- Database pool settings (connections, lifetime)
- Session and rate limiting settings

Update all files to use these constants instead of hardcoded values.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

5 files changed, 65 insertions, 10 deletions

diff --git a/internal/api/http.go b/internal/api/http.go
index df28c65..d9ddf0e 100644
--- a/internal/api/http.go
+++ b/internal/api/http.go
@@ -7,7 +7,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"time"
+
+	"task-dashboard/internal/config"
 )
 
 // BaseClient provides common HTTP functionality for API clients
@@ -19,7 +20,7 @@ type BaseClient struct {
 // NewBaseClient creates a new BaseClient with default settings
 func NewBaseClient(baseURL string) BaseClient {
 	return BaseClient{
-		HTTPClient: &http.Client{Timeout: 15 * time.Second},
+		HTTPClient: &http.Client{Timeout: config.HTTPClientTimeout},
 		BaseURL:    baseURL,
 	}
 }
diff --git a/internal/api/trello.go b/internal/api/trello.go
index 67ffad0..a276726 100644
--- a/internal/api/trello.go
+++ b/internal/api/trello.go
@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"task-dashboard/internal/config"
 	"task-dashboard/internal/models"
 )
 
@@ -170,7 +171,7 @@ func (c *TrelloClient) GetBoardsWithCards(ctx context.Context) ([]models.Board,
 
 	var wg sync.WaitGroup
 	var mu sync.Mutex // Protects writes to boards slice elements
-	sem := make(chan struct{}, 5) // Limit to 5 concurrent requests
+	sem := make(chan struct{}, config.MaxConcurrentTrelloRequests)
 
 	for i := range boards {
 		wg.Add(1)
diff --git a/internal/config/constants.go b/internal/config/constants.go
new file mode 100644
index 0000000..a199404
--- /dev/null
+++ b/internal/config/constants.go
@@ -0,0 +1,51 @@
+package config
+
+import "time"
+
+// Concurrency limits
+const (
+	// MaxConcurrentTrelloRequests limits parallel Trello API calls
+	MaxConcurrentTrelloRequests = 5
+)
+
+// Timeouts
+const (
+	// HTTPClientTimeout is the default timeout for HTTP clients
+	HTTPClientTimeout = 15 * time.Second
+
+	// GoogleCalendarInitTimeout is the timeout for Google Calendar initialization
+	GoogleCalendarInitTimeout = 30 * time.Second
+
+	// GracefulShutdownTimeout is the timeout for server graceful shutdown
+	GracefulShutdownTimeout = 10 * time.Second
+
+	// RequestTimeout is the timeout for individual HTTP requests
+	RequestTimeout = 60 * time.Second
+)
+
+// Default meal times (24-hour format)
+const (
+	BreakfastHour = 8
+	LunchHour     = 12
+	DinnerHour    = 19
+)
+
+// Database connection pool settings
+const (
+	SQLiteMaxOpenConns    = 5
+	SQLiteMaxIdleConns    = 2
+	SQLiteConnMaxLifetime = time.Hour
+)
+
+// Session settings
+const (
+	SessionLifetime = 24 * time.Hour
+)
+
+// Rate limiting
+const (
+	// AuthRateLimitRequests is max login attempts per window
+	AuthRateLimitRequests = 5
+	// AuthRateLimitWindow is the time window for rate limiting
+	AuthRateLimitWindow = 15 * time.Minute
+)
diff --git a/internal/handlers/timeline_logic.go b/internal/handlers/timeline_logic.go
index c51262a..0d4595f 100644
--- a/internal/handlers/timeline_logic.go
+++ b/internal/handlers/timeline_logic.go
@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"task-dashboard/internal/api"
+	"task-dashboard/internal/config"
 	"task-dashboard/internal/models"
 	"task-dashboard/internal/store"
 )
@@ -49,13 +50,13 @@ func BuildTimeline(ctx context.Context, s *store.Store, calendarClient api.Googl
 		// Apply Meal Defaults
 		switch meal.MealType {
 		case "breakfast":
-			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), 8, 0, 0, 0, mealTime.Location())
+			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), config.BreakfastHour, 0, 0, 0, mealTime.Location())
 		case "lunch":
-			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), 12, 0, 0, 0, mealTime.Location())
+			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), config.LunchHour, 0, 0, 0, mealTime.Location())
 		case "dinner":
-			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), 19, 0, 0, 0, mealTime.Location())
+			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), config.DinnerHour, 0, 0, 0, mealTime.Location())
 		default:
-			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), 12, 0, 0, 0, mealTime.Location())
+			mealTime = time.Date(mealTime.Year(), mealTime.Month(), mealTime.Day(), config.LunchHour, 0, 0, 0, mealTime.Location())
 		}
 
 		item := models.TimelineItem{
diff --git a/internal/store/sqlite.go b/internal/store/sqlite.go
index 12aa1ce..c2f6e98 100644
--- a/internal/store/sqlite.go
+++ b/internal/store/sqlite.go
@@ -13,6 +13,7 @@ import (
 
 	_ "github.com/mattn/go-sqlite3"
 
+	"task-dashboard/internal/config"
 	"task-dashboard/internal/models"
 )
 
@@ -47,9 +48,9 @@ func New(dbPath, migrationDir string) (*Store, error) {
 
 	// Configure connection pool for SQLite with WAL mode
 	// WAL allows concurrent reads, but writes still need serialization
-	db.SetMaxOpenConns(5)
-	db.SetMaxIdleConns(2)
-	db.SetConnMaxLifetime(time.Hour)
+	db.SetMaxOpenConns(config.SQLiteMaxOpenConns)
+	db.SetMaxIdleConns(config.SQLiteMaxIdleConns)
+	db.SetConnMaxLifetime(config.SQLiteConnMaxLifetime)
 
 	store := &Store{db: db, migrationDir: migrationDir}