Add Loop block functionality

[defsanmith]

Problem / Motivation TypeBot currently has no native mechanism to repeat a sequence of blocks. Builders are forced to:

• Duplicate blocks manually
• Inject custom JavaScript
• Abandon certain use-cases altogether A first-class Loop Block lets flows iterate over a list or repeat until a condition is met, unlocking multi-item data capture, retry logic, dynamic surveys, and more.

Proposed Solution Add a Loop (Iteration) Block that can wrap any sub-flow and execute it repeatedly based on iterations = n; exits when counter reaches zero

Builder UX

• Drag-and-drop "Loop" container; creators can next blocks inside.
• The side panel shows a loop model dropdown and configurable parameters.
• Visual badge displays current mode, e.g., For-Each.

Runtime behavior

• Maintains loop index (loop.index, loop.item) in conversation state.
• Supports a break via a "Break Loop" exit inside nested blocks.
• Hard guardrail maxIterations to prevent infinite loops.