Configure portable Neovim classroom and Herdr SSH setup

[thefoxkai]

What changed

• sync the recent macOS Ghostty, shell, and Neovim plugin updates
• modernize Neovim 0.12 LSP setup for basedpyright, Ruff, texlab, and clangd
• add manual C/C++ formatting and a project-aware :RunTests command
• install the complete classroom toolchain on macOS and Debian/Ubuntu
• install and configure Herdr while keeping tmux as an independent fallback
• use OSC52 clipboard handling in both SSH and persistent Herdr panes

Cross-machine safeguards

• C/C++ formatting stays manual, so opening an existing repository cannot reformat it on save
• CMake test runs keep compile_commands.json inside build/ and do not dirty repository roots
• Linux upgrades old Neovim installations to the shared tested 0.12 baseline
• shell paths use $HOME and optional OpenClaw completion is guarded

Validation

• Python uv run pytest path passed on a real project
• CMake configure, build, and CTest path passed on a throwaway C++ project
• basedpyright, Ruff, and clangd attached live; clang-format was available manually
• Tree-sitter parsers compiled and loaded
• Herdr 0.8.2 is running and its shared config passes validation
• bash -n, zsh -n, headless Neovim startup, and git diff --check passed

One physical Ghostty-to-Mac OSC52 copy remains best verified during the next real SSH session.