Add a new bot

[CarsonL15]

As an admin, I want to register a new bot in the system, so that newly deployed robots can start receiving orders.

Acceptance criteria:

• A form accepts a bot name, initial battery level (0 to 100), and online status
• Submitting calls POST /api/bots
• On success the new bot appears in the fleet list
• Validation errors from the API are shown inline
• Duplicate or invalid names are rejected gracefully