feat: isolate profanity filter with separate database

- Create dedicated ProfanityFilter class with isolated SQLite database
- Separate profanity.db from main application database to prevent SQLITE_MISUSE errors
- Add comprehensive custom word management (CRUD operations)
- Implement advanced profanity detection with leetspeak and pattern matching
- Add admin UI for managing custom profanity words
- Add extensive test suites for both profanity filter and API routes
- Update server.js to use isolated profanity filter
- Add proper database initialization and cleanup methods
- Support in-memory databases for testing

Breaking changes:
- Profanity filter now uses separate database file
- Updated admin API endpoints for profanity management
- Enhanced profanity detection capabilities

jest.config.js

@@ -0,0 +1,17 @@
+module.exports = {
+  testEnvironment: 'node',
+  collectCoverageFrom: [
+    '**/*.js',
+    '!**/node_modules/**',
+    '!**/coverage/**',
+    '!**/public/**',
+    '!jest.config.js',
+    '!server.js' // Exclude main server file as it's integration-focused
+  ],
+  testMatch: [
+    '**/tests/**/*.test.js',
+    '**/tests/**/*.spec.js'
+  ],
+  verbose: true,
+  setupFilesAfterEnv: ['<rootDir>/tests/setup.js']
+};