Remove outdated legacy vs maximized board documentation and update flash tool references

The documentation contained extensive references to "Legacy vs Maximized boards" that are no longer relevant and were confusing newcomers. Since all current Heads boards now use what was previously called the "maximized" approach, this distinction has become obsolete. ## Changes Made **Prerequisites.md:** - Replaced the lengthy "Legacy vs Maximized boards" section with a concise "Board Architecture Overview" - Clearly states that all current boards use modern architecture with deactivated ME and unlocked IFD - Corrected ME statement to clarify that neutering is only possible on older platforms (up to Ivy Bridge), while newer platforms use HAP bits or other deactivation methods - Replaced problematic collapsible section with clean link to dedicated historical page **Upgrading.md:** - Simplified the migration section and replaced collapsible content with link to dedicated historical page - Updated verification steps to focus on current vs. very old firmware rather than legacy vs. maximized - Updated flash tool references to use `flashprog` for newer firmware (2025+) with fallback to `flashrom` for older versions - Maintained important safety warnings while reducing complexity **Development/Porting.md:** - Fixed broken link reference to the removed Prerequisites section - Updated technical language to reflect current board architecture **Building-Heads documentation:** - Updated p8z77-m_pro-tpm1.maximized.md and x230-maximized.md - Removed confusing "as opposed to legacy boards" comparisons **About/Historical-Legacy-Migration.md (New):** - Created dedicated page for all historical legacy board information - Includes complete legacy board details, migration steps, and technical information - Properly formatted with table of contents and clear section headers - Resolves formatting issues that occurred with collapsible sections - Updated flash tool references to reflect flashrom→flashprog transition **configuring-keys.md:** - Updated flash tool completion references to be generic about which tool is used based on firmware version ## Impact This change eliminates confusion for newcomers by: - Clearly communicating that all current boards use unified, modern architecture - Removing references to non-existent "legacy" board variants - Preserving historical context in a dedicated, properly formatted page for edge cases where users might be upgrading from very old firmware - Fixing technical inaccuracies about ME handling across different Intel platform generations - Ensuring accurate flash tool references for both current (flashprog) and older (flashrom) firmware versions The documentation now accurately reflects the current state of the Heads repository where all supported boards use the approach that was previously distinguished as "maximized," with platform-appropriate ME deactivation methods and correct flash tool references. Fixes #204. <!-- START COPILOT CODING AGENT TIPS --> --- 💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more [Copilot coding agent tips](https://gh.io/copilot-coding-agent-tips) in the docs.