feat(tui): add /tools command for listing available tools

[Om-Beast]

Summary

This PR adds a new /tools REPL command that allows users to inspect the agent's available tools directly from the interactive session.

To keep the tool registry as the single source of truth, I introduced a small exported Agent.ToolList() accessor backed by Registry.ToolList(), exposing each tool's name, description, and mutating status without leaking the registry itself.

The /tools command has been wired into the existing slash-command menu and displays each registered tool together with its one-line description and whether it is Read-only or Permission-gated.

Type of change

• feat — new feature
• fix — bug fix
• refactor — internal change, no user-visible behavior change
• docs — documentation only
• test — tests only
• chore — tooling, CI, deps
• perf — performance improvement
• breaking change — incompatible change

Test plan

• Added a test covering the /tools slash command.
• Built the project successfully using go build ./....
• Ran go test ./internal/tui to verify the implementation. The /tools changes did not introduce any new failures; existing unrelated test failures remain in the repository.

Checklist

• Tests added or updated
• Coverage is still ≥ 90% (make cover-gate) (not verified locally)
• make lint and make docker-test are green locally (not run locally)
• Documentation updated if user-facing behavior changed

Design notes

• Preserves the registry as the single source of truth.
• Exposes tool metadata through a minimal Agent.ToolList() accessor.
• Preserves tool registration order in the displayed list.
• Integrates cleanly with the existing REPL slash-command infrastructure.

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