CLI: Allow hypens in agent name with `arctl agent init`

[shashankram]

$ arctl agent init adk python test-agent
Error: invalid agent name: "test-agent" is not a valid Python identifier: must start with a letter or underscore and contain only letters, digits, and underscores

[groundnuty]

Submitted a fix in #205.

Changes:

• Relaxed agentNameRegex to ^[a-zA-Z][a-zA-Z0-9-]*[a-zA-Z0-9]$
• Dots remain excluded to avoid .well-known URL path ambiguity
• Added PythonSafeName() helper to convert hyphens to underscores for Python code generation
• Python generator converts the name before rendering templates so packages stay importable

Database constraint already allows hyphens, so no migration needed.