Introduce dual-track course structure and add day/evening course maps - #12

Motivation

• Consolidate course materials into a single reusable repository that supports two distinct teaching tracks (day and evening).
• Provide clear, non-destructive routing so existing module links and Colab references remain valid while allowing separate weekly maps and assessment guidance.
• Improve documentation discoverability by surfacing class-specific maps in the docs index.

Description

• Update top-level README.md to describe the dual-track course intent, add a selection table for class routes, and adjust the main navigation.
• Add courses/README.md to define the "one repository, two tracks" architecture, maintenance rules, and naming/semester guidelines.
• Add courses/day/README.md with the day-track syllabus, recommended unit order, project minimums, and support items to be added.
• Add courses/evening/README.md with the evening-track syllabus emphasizing Python→API→cloud workflow, unit sequence, assessment checkpoints, and grading guidance.
• Update docs/README.md to include links to the new course map pages and reorganize the docs index accordingly.

Testing

• No automated tests were added or modified because this change is documentation-only.
• No documentation build or link-check jobs were executed as part of this PR.

Codex Task