feat: Add --show-thinking flag to CLI (#311) and Show Tool Outputs in a Collapsible Pane #326

[dayal-arnav05]

Add support for displaying agent reasoning/thinking process in the CLI.

Changes:

• Add --show-thinking command-line flag to main.py
• Extend SessionState with show_thinking field in config.py
• Display reasoning blocks in dim style when flag is enabled in execution.py
• Update help documentation and examples in ui.py

When enabled with --show-thinking, the agent's reasoning blocks from LangChain content blocks are displayed in real-time as dim text, providing transparency into the agent's thought process.

Resolves #311