Refactor docs into structured hierarchy with learning materials

[Copilot]

Documentation was flat with mixed concerns - architecture, roadmap, learning notes, and boot guides all at /docs/*.md. No tracking of development progress or learning journey.

Changes

Directory structure - 9 subdirectories by purpose:

• /architecture - System design and implementation
• /roadmap - Development planning and milestones
• /refactoring - Code reorganization history
• /boot - Bootloader and multiboot documentation
• /virtualization - VM setup and troubleshooting
• /chapters - Chapter-based learning materials (7 chapters)
• /learning - Learning index tracking phase progress
• /journal - Development log with structured entries
• /research - Reserved for future research notes

Moved files - 12 existing docs to appropriate subdirectories using git mv:

• ARCHITECTURE.md → /architecture/
• architecture.md → /architecture/system_overview.md (resolved naming inconsistency)
• Multiboot docs → /boot/
• VirtualBox docs → /virtualization/
• Roadmap docs → /roadmap/
• Refactoring docs → /refactoring/

Learning materials - 7 comprehensive chapters covering Phase 0 through future work:

• CH00: Foundations (boot, protected mode, GDT)
• CH01: Memory (PMM, VMM, paging)
• CH02: Interrupts (IDT, exceptions, PIC)
• CH03-06: Scheduler, processes, security, Rust (planned/future)

Each chapter includes: phase alignment, objectives, concepts studied, implementation status, open questions, next actions.

Documentation index - /docs/README.md defines:

• Purpose and audience for each subdirectory
• Distinction between architecture vs chapters vs roadmap vs journal
• Documentation standards (tone, formatting, naming)
• Contribution guidelines for new docs

Learning control - /learning/LEARNING_INDEX.md tracks:

• Current phase and focus areas
• Completed chapters and active research
• Skills acquired and knowledge gaps
• Learning resources and methodology

Development journal - /journal/DEVELOPMENT_LOG.md provides:

• Structured template (date/learned/implemented/issues/invariants)
• Historical Phase 0 summary
• Guidelines for journal entries and commit messages

Updated references:

• Root README.md - Reorganized documentation section with categorized links
• CONTRIBUTING.md - Updated roadmap reference
• /refactoring/KERNEL_REFACTORING_SUMMARY.md - Fixed internal paths

Git history preserved for all moved files. No kernel code modified.

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