refactor: consolidate chat into swarm_control everywhere

fix(orchestration): resolve skill hallucination, brace crashes, and silent turns in swarm control ...

- Implemented strictly-worded 'Tool-belt' in system prompt to prevent hallucinating external skills.
- Replaced fragile .format() with robust .replace() for system prompts to prevent crashes on curly braces.
- Optimized TTS streaming: increased concurrency and reduced chunk sizes to eliminate mid-sentence pauses.
- Fixed 'silent turn' bug in Swarm Control by ensuring fallback content is yielded even if AI only produces reasoning/tools.
- Improved history formatting to handle assistant turns mapping to tool calls without main content.
- Corrected Gemini model fallback to gemini-1.5-flash.