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/queries/session.sql

@@ -0,0 +1,23 @@
+-- name: CreateSession :one
+INSERT INTO sessions (token, ip_address, user_agent, client_type, expires_at)
+VALUES ($1, $2, $3, $4, $5)
+RETURNING token, ip_address, user_agent, client_type, expires_at, created_at;
+
+-- name: GetSession :one
+SELECT token, ip_address, user_agent, client_type, expires_at, created_at
+FROM sessions
+WHERE token = $1
+LIMIT 1;
+
+-- name: DeleteSession :exec
+DELETE FROM sessions
+WHERE token = $1;
+
+-- name: DeleteExpiredSessions :exec
+DELETE FROM sessions
+WHERE expires_at < NOW();
+
+-- name: ListSessions :many
+SELECT token, ip_address, user_agent, client_type, expires_at, created_at
+FROM sessions
+ORDER BY created_at DESC;