Uplift concrete security UI

[kcelia]

What does this PR do? Add aTLS security indicator for concrete-security provider

Show connection security status in the assistant message header:

🔐 Secure (green) when aTLS attestation succeeds
⚠ Unsecure (red) when the connection fails
Only applies to the concrete-security provider; other providers display
unchanged.

How did you verify your code works? via a tests

How to test? cd ~/secure-opencode/packages/opencode && bun test test/cli/tui/provider.test.ts

[github-actions]

Hey! Your PR title Uplift concrete security UI doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.