Add account character context and smarter Twitter prompts

[ahmadhozien]

Closes #207

What changed

• added a persistent character_context field to Twitter and YouTube accounts
• prompted to backfill missing context on existing accounts
• passed account context into Twitter and YouTube prompt generation
• added dialect-aware Twitter prompting and stricter cleanup/quality checks for generated tweets
• updated docs and example config for dialect and account context usage

Validation

• venv\\Scripts\\python.exe -m py_compile src\\config.py src\\cache.py src\\main.py src\\classes\\Twitter.py src\\classes\\YouTube.py