feat: enable dynamic tool selection in architect mode for context discovery

- Remove hardcoded suggestions for read_file/search_files in architect mode
- Replace with generic 'using provided tools' to allow dynamic selection
- Enables architect mode to leverage codebase_search when available
- Promotes more intelligent tool selection based on available capabilities
- Updates test snapshots to reflect the instruction changes

This change allows architect mode to adapt to the presence of different tools,
particularly benefiting from semantic search via codebase_search when indexed.

Author: hannesrudolph