feat: Implement Session Token System with /api/v1 base path

- Add migration 000004 for sessions table and performance indexes
- Create session.sql queries for CRUD operations
- Generate session repository code with sqlc
- Create token auth middleware for Echo framework
- Create token handler with create/delete/cleanup endpoints
- Add /api/v1 router with token authentication infrastructure
- Update dbHelper.go to use Up() instead of Migrate(2)
- Update server.go to initialize token handler
- Existing endpoints remain functional (to be deprecated)

New endpoints:
- POST /api/v1/token - Create new session token
- DELETE /api/v1/token - Invalidate token
- POST /api/v1/token/cleanup - Remove expired sessions

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/db/repository/models.go

@@ -6,6 +6,8 @@ package repository
 
 import (
 	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
 )
 
 type Game struct {
@@ -21,6 +23,15 @@ type Game struct {
 	Hash          string     `json:"hash"`
 }
 
+type Session struct {
+	Token      string             `json:"token"`
+	IpAddress  string             `json:"ip_address"`
+	UserAgent  string             `json:"user_agent"`
+	ClientType *string            `json:"client_type"`
+	ExpiresAt  pgtype.Timestamptz `json:"expires_at"`
+	CreatedAt  pgtype.Timestamptz `json:"created_at"`
+}
+
 type Song struct {
 	GameID      int32   `json:"game_id"`
 	SongName    string  `json:"song_name"`