Simplify agent wrapping using WorkflowBuilder pattern

[thegovind]

• Agents are currently wrapped explicitly in AgentExecutor.
• Consider using WorkflowBuilder().set_start_executor(...).add_edge(...).build() for simpler wiring.

Acceptance Criteria:

• Agent wrapping and workflow construction uses the builder pattern where possible.
• Code is more declarative and easier to follow.
• Any necessary documentation is updated.