feat: remove start.sh script and add appearance preferences management

- Deleted the start.sh script for container management.
- Added AGENTS.md for project guidelines and development principles.
- Introduced new SQL migration files for user appearance preferences and platform settings.
- Implemented appearance provider to manage user interface themes and preferences.
- Created branding utility to define and manage branding-related constants and types.

Co-authored-by: Copilot <copilot@github.com>

drizzle/0005_platform_settings_and_roles.sql

@@ -0,0 +1,59 @@
+ALTER TABLE "beenvoice_user"
+ADD COLUMN "role" varchar(20) DEFAULT 'user' NOT NULL;
+--> statement-breakpoint
+UPDATE "beenvoice_user"
+SET "role" = 'admin'
+WHERE "id" = (
+  SELECT "id"
+  FROM "beenvoice_user"
+  ORDER BY "createdAt" ASC
+  LIMIT 1
+);
+--> statement-breakpoint
+CREATE TABLE IF NOT EXISTS "beenvoice_platform_setting" (
+  "id" varchar(50) PRIMARY KEY DEFAULT 'global' NOT NULL,
+  "brandName" varchar(100) DEFAULT 'beenvoice' NOT NULL,
+  "brandTagline" varchar(255) DEFAULT 'Simple and efficient invoicing for freelancers and small businesses' NOT NULL,
+  "brandLogoText" varchar(100) DEFAULT 'beenvoice' NOT NULL,
+  "brandIcon" varchar(20) DEFAULT '$' NOT NULL,
+  "colorTheme" varchar(50) DEFAULT 'slate' NOT NULL,
+  "customColor" varchar(50),
+  "theme" varchar(20) DEFAULT 'system' NOT NULL,
+  "interfaceTheme" varchar(50) DEFAULT 'beenvoice' NOT NULL,
+  "bodyFontPreference" varchar(50) DEFAULT 'brand' NOT NULL,
+  "headingFontPreference" varchar(50) DEFAULT 'brand' NOT NULL,
+  "radiusPreference" varchar(20) DEFAULT 'xl' NOT NULL,
+  "sidebarStyle" varchar(20) DEFAULT 'floating' NOT NULL,
+  "createdAt" timestamp DEFAULT now() NOT NULL,
+  "updatedAt" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+INSERT INTO "beenvoice_platform_setting" (
+  "id",
+  "brandName",
+  "brandTagline",
+  "brandLogoText",
+  "brandIcon",
+  "colorTheme",
+  "customColor",
+  "theme",
+  "interfaceTheme",
+  "bodyFontPreference",
+  "headingFontPreference",
+  "radiusPreference",
+  "sidebarStyle"
+) VALUES (
+  'global',
+  'beenvoice',
+  'Simple and efficient invoicing for freelancers and small businesses',
+  'beenvoice',
+  '$',
+  'slate',
+  NULL,
+  'system',
+  'beenvoice',
+  'brand',
+  'brand',
+  'xl',
+  'floating'
+) ON CONFLICT ("id") DO NOTHING;