M27.6: Update --init wizard for expertise and mode selection

[bug-ops]

Parent: #590
Blocked by: M27.1

Scope

Add interactive prompts to the --init configuration wizard for:

1. Expertise level selection — explain each option, default: intermediate
2. Interaction mode selection — explain each option, default: assistant

Follow existing wizard patterns (dialoguer prompts).

Acceptance Criteria

• Both prompts appear during --init flow
• Selected values written to config TOML
• Default values work when user presses Enter
• Descriptions help user make informed choice