feat: add advanced settings gate to agent creation wizard

[tejaskash]

Summary

• Adds a "Configure advanced settings?" Yes/No gate before network configuration in the agent creation wizard (both Create and BYO paths)
• Defaults to "No, use defaults" (Public network, no VPC), letting most users skip network config with one Enter press
• Selecting "Yes, customize" expands into the existing network mode, subnet, and security group steps

Screenshots

Advanced gate (defaults to "No")

Default path: skips to Confirm with PUBLIC network

"Yes, customize" expands network config

Test plan

• Default path: Enter on Advanced → Confirm shows "Network: PUBLIC"
• Advanced Yes: Yes → Network → VPC → Subnets → SGs → Confirm reflects VPC config
• Back navigation: Esc from Network → Advanced; Esc from Advanced → Memory
• State cleanup: Yes → VPC config → back → No → Confirm shows PUBLIC, no VPC
• MCP protocol: Select MCP → Advanced step still appears (skips Framework/Model as expected)
• BYO path: Bedrock → Advanced gate → defaults → Confirm shows PUBLIC
• Unit tests: 2510/2510 passing (2 pre-existing PTY failures unrelated)
• E2E: container-strands-bedrock test fails — pre-existing on main, unrelated to this change

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	43.94%	5004 / 11388
🔵	Statements	43.61%	5309 / 12173
🔵	Functions	43.99%	934 / 2123
🔵	Branches	44.98%	3199 / 7112

Generated in workflow #1105 for commit 5d282ef by the Vitest Coverage Report Action

[notgitika]

Can we add unit tests for this new step logic? Also, I believe "Protocol" should also fall under Advanced... lmk what you think.

Other concerns:
State cleanup inconsistency between Generate and BYO paths

useGenerateWizard.ts clears VPC config with undefined, but AddAgentScreen.tsx clears with empty strings ''. If downstream code checks !== undefined or serializes to JSON, behavior will diverge. Should use the same sentinel value in both paths.

ADVANCED_OPTIONS has description: undefined for "Yes, customize"

Other option arrays use actual strings for all descriptions. If WizardSelect renders description without a null check, this could render "undefined" as text. Should be description: ' ' or verified against the component's rendering logic.

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