feat(nodes): add conditional if/else branching node (#628)

[dsapandora]

Summary

Introduces a conditional routing node that evaluates a sandboxed Python expression
against incoming text/questions content and directs it to one of two exclusive
branches (then / else) via selectBranch dispatch filtering in the Binder.
Downstream nodes receive standard writeText/writeQuestions calls unchanged.

Engine:

• selectBranch() / clearBranchSelection() on Binder
• m_branchMap tagging instances per branch
• Meta-lane expansion in bind(): binding "then" or "else" auto-binds all data lanes
  and tags the instance
• "then" / "else" added to MethodNames for pipeline-config validation
• Python bindings for the two new callbacks

Node (nodes/src/nodes/conditional/):

• Single profile: Python expression evaluated per write
• Scope exposes the incoming content: text on the text lane, questions on the
  questions lane
• Truthy → then; falsy → else; runtime error → else (logged)
• Supports text and questions lanes

Type

Feature

Testing

• Tests added or updated
• Tested locally
• ./builder test passes

Checklist

• Commit messages follow conventional commits
• No secrets or credentials included
• Wiki updated (if applicable)
• Breaking changes documented (if applicable)

Linked Issue

Related to #628

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[github-actions]

No description provided.

[Rod-Christensen]

We need to examine this as this breaks the lane architecture