feat: Add i18n Multilingual Support (English, Telugu, Hindi)

CORE INFRASTRUCTURE: • i18next + react-i18next + language detector • i18n.ts with 11 namespaces (common, auth, patient, medical, dashboard, forms, roles, notifications, realtime, camp, validation) • i18n-types.ts with TypeScript types and module augmentation • LanguageSwitcher component with shadcn Dropdown • useLanguagePersistence hook for route persistence • medical-glossary.ts with 100+ healthcare terms

TRANSLATION FILES (540+ keys): • English (en) - Complete • Telugu (te) - Complete • Hindi (hi) - Complete

PAGES 100% TRANSLATED (5): ✅ LoginPage - All forms, buttons, validation messages ✅ DashboardPage - All tabs, role labels, action buttons ✅ AssignDoctorPage - Book search, doctor selection, confirmation ✅ ConsultationQueuePage - Queue display, filter toggles ✅ CounselingPage - Book search, patient details, completion

PAGES PARTIALLY TRANSLATED (4): ⏳ PatientRegistrationPage - Landing page ✅ ⏳ RecordVitalsPage - Book search section ✅ ⏳ VerifyMedicinesPage - Book search section ✅ ⏳ UpdatePrescriptionPage - Book search section ✅

REMAINING WORK: 16 pages (55% complete)

DOCUMENTATION: 📄 I18N_GUIDE.md - Complete user/developer guide 📄 I18N_TEAM_GUIDE.md - Team onboarding documentation

TESTING: • Build passes ✅ • Language switcher works ✅ • Telugu/Hindi translations load ✅ • Some unit tests need i18n mock updates (known issue)