AppForge: migrate off Supabase to external Postgres + Better Auth + local storage

- New Express + TypeScript backend (server/) with pg, Better Auth, local file storage
- De-Supabased Postgres schema (server/db) and TS reimplementations of DB functions
- Frontend data layer rewired to REST (rest-client + backend-client compat shim)
- Removed all Supabase references (code, config, deps, docs)
- New brand assets: gradient favicon/app icons + dark/white wordmark logos

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/db/auth-schema.sql

@@ -0,0 +1,52 @@
+-- Better Auth core schema (v1.x). Identifiers are camelCase and quoted to
+-- match Better Auth's default field->column mapping.
+
+CREATE TABLE IF NOT EXISTS "user" (
+  "id" text PRIMARY KEY,
+  "name" text NOT NULL DEFAULT '',
+  "email" text NOT NULL UNIQUE,
+  "emailVerified" boolean NOT NULL DEFAULT false,
+  "image" text,
+  "createdAt" timestamptz NOT NULL DEFAULT now(),
+  "updatedAt" timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE TABLE IF NOT EXISTS "session" (
+  "id" text PRIMARY KEY,
+  "expiresAt" timestamptz NOT NULL,
+  "token" text NOT NULL UNIQUE,
+  "createdAt" timestamptz NOT NULL DEFAULT now(),
+  "updatedAt" timestamptz NOT NULL DEFAULT now(),
+  "ipAddress" text,
+  "userAgent" text,
+  "userId" text NOT NULL REFERENCES "user"("id") ON DELETE CASCADE
+);
+
+CREATE TABLE IF NOT EXISTS "account" (
+  "id" text PRIMARY KEY,
+  "accountId" text NOT NULL,
+  "providerId" text NOT NULL,
+  "userId" text NOT NULL REFERENCES "user"("id") ON DELETE CASCADE,
+  "accessToken" text,
+  "refreshToken" text,
+  "idToken" text,
+  "accessTokenExpiresAt" timestamptz,
+  "refreshTokenExpiresAt" timestamptz,
+  "scope" text,
+  "password" text,
+  "createdAt" timestamptz NOT NULL DEFAULT now(),
+  "updatedAt" timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE TABLE IF NOT EXISTS "verification" (
+  "id" text PRIMARY KEY,
+  "identifier" text NOT NULL,
+  "value" text NOT NULL,
+  "expiresAt" timestamptz NOT NULL,
+  "createdAt" timestamptz NOT NULL DEFAULT now(),
+  "updatedAt" timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX IF NOT EXISTS idx_session_user ON "session" ("userId");
+CREATE INDEX IF NOT EXISTS idx_account_user ON "account" ("userId");
+CREATE INDEX IF NOT EXISTS idx_verification_identifier ON "verification" ("identifier");