Provide guided path to codebase newcomers

Parent User Story: As a student new to a codebase, I want opencode to give me a guided starting path through the project by highlighting important entry points and showing how a typical feature or request flows through the codebase, so that I can build a mental model of the system without having to inspect every file myself.

Estimated effort: 12 hours
Size: M-L
Dependencies: The entire codebase
Initial Assignment: Access how opencode currently does the user story in plan mode and edit mode
Milestone: Sprint 2

Acceptance criteria:

• When Learn Mode is enabled, opencode identifies and summarizes the major components of the codebase with clear separation of concerns.
• opencode categorizes relevant files/directories into areas such as frontend, backend, testing, configuration, and application logic when applicable.
• opencode identifies important entry-point files that a newcomer should inspect first.
• opencode identifies areas in the codebase user shouldn't spend time on
• opencode can trace at least one representative feature or request through the codebase, showing the major files/functions involved in order.
• opencode presents guidance in clear, beginner-friendly language and avoids complex technical jargon.