Reorganize repository into monorepo structure

Restructured the project to support multiple frontend applications:
- Move web app to web/ directory
- Create pezkuwi-sdk-ui/ for Polkadot SDK clone (planned)
- Create mobile/ directory for mobile app development
- Add shared/ directory with common utilities, types, and blockchain code
- Update README.md with comprehensive documentation
- Remove obsolete DKSweb/ directory

This monorepo structure enables better code sharing and organized
development across web, mobile, and SDK UI projects.

web/supabase/migrations/004_create_upsert_function.sql

@@ -0,0 +1,97 @@
+-- ========================================
+-- Create Secure Upsert Function for Profiles
+-- ========================================
+-- Uses SECURITY DEFINER to bypass RLS for authenticated users
+
+-- First, ensure username is nullable
+ALTER TABLE public.profiles
+  ALTER COLUMN username DROP NOT NULL;
+
+ALTER TABLE public.profiles
+  ALTER COLUMN username SET DEFAULT '';
+
+-- Create secure upsert function
+CREATE OR REPLACE FUNCTION public.upsert_user_profile(
+  p_username TEXT DEFAULT '',
+  p_full_name TEXT DEFAULT NULL,
+  p_bio TEXT DEFAULT NULL,
+  p_phone_number TEXT DEFAULT NULL,
+  p_location TEXT DEFAULT NULL,
+  p_website TEXT DEFAULT NULL,
+  p_language TEXT DEFAULT 'en',
+  p_theme TEXT DEFAULT 'dark',
+  p_notifications_email BOOLEAN DEFAULT true,
+  p_notifications_push BOOLEAN DEFAULT false,
+  p_notifications_sms BOOLEAN DEFAULT false
+)
+RETURNS public.profiles AS $$
+DECLARE
+  result public.profiles;
+BEGIN
+  -- Use auth.uid() to ensure user can only upsert their own profile
+  INSERT INTO public.profiles (
+    id,
+    username,
+    full_name,
+    bio,
+    phone_number,
+    location,
+    website,
+    language,
+    theme,
+    notifications_email,
+    notifications_push,
+    notifications_sms,
+    updated_at
+  )
+  VALUES (
+    auth.uid(),
+    p_username,
+    p_full_name,
+    p_bio,
+    p_phone_number,
+    p_location,
+    p_website,
+    p_language,
+    p_theme,
+    p_notifications_email,
+    p_notifications_push,
+    p_notifications_sms,
+    NOW()
+  )
+  ON CONFLICT (id)
+  DO UPDATE SET
+    username = COALESCE(NULLIF(EXCLUDED.username, ''), profiles.username, ''),
+    full_name = COALESCE(EXCLUDED.full_name, profiles.full_name),
+    bio = COALESCE(EXCLUDED.bio, profiles.bio),
+    phone_number = COALESCE(EXCLUDED.phone_number, profiles.phone_number),
+    location = COALESCE(EXCLUDED.location, profiles.location),
+    website = COALESCE(EXCLUDED.website, profiles.website),
+    language = COALESCE(EXCLUDED.language, profiles.language),
+    theme = COALESCE(EXCLUDED.theme, profiles.theme),
+    notifications_email = COALESCE(EXCLUDED.notifications_email, profiles.notifications_email),
+    notifications_push = COALESCE(EXCLUDED.notifications_push, profiles.notifications_push),
+    notifications_sms = COALESCE(EXCLUDED.notifications_sms, profiles.notifications_sms),
+    updated_at = NOW()
+  RETURNING *
+  INTO result;
+
+  RETURN result;
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;
+
+-- Grant execute permission to authenticated users only
+GRANT EXECUTE ON FUNCTION public.upsert_user_profile TO authenticated;
+
+-- Revoke from public for security
+REVOKE EXECUTE ON FUNCTION public.upsert_user_profile FROM PUBLIC;
+
+-- Success message
+DO $$
+BEGIN
+  RAISE NOTICE '========================================';
+  RAISE NOTICE 'Profile upsert function created successfully!';
+  RAISE NOTICE 'Function: upsert_user_profile()';
+  RAISE NOTICE 'This bypasses RLS using SECURITY DEFINER';
+  RAISE NOTICE '========================================';
+END $$;