feat: source ~/.myfiles/shell/claude.zsh from .zshrc

[tamakiii-doppelganger]

Summary

• Add one source line to .zshrc that activates the claude() shell function shipped in tamakiii/myfiles#219.
• The guard [[ -f ~/.myfiles/shell/claude.zsh ]] keeps .zshrc loadable on hosts where the myfiles half hasn't been installed yet.

Context

tamakiii/myfiles#219 added shell/claude.zsh defining a claude() function that injects --add-dir <path> for each existing default path (~/.myfiles, ~/Documents/Obsidian/tamakiii-hdd, ~/Git/tamakiii/meta/main) before exec'ing the real binary via command claude. Without a sourcing line in .zshrc, the file is inert. This PR is that one-line companion.

The split exists because ~/.myfiles owns the launcher logic (private half of the dotfiles system) while ~/.dotfiles owns shell init.

Test plan

• After merge + make install from ~/.dotfiles: open a fresh shell and run type claude. Should report claude is a shell function from /home/tamakiii/.myfiles/shell/claude.zsh instead of pointing at ~/.local/bin/claude.
• claude --version should still print the version (the wrapper passes args through and execs the real binary).
• On a host without ~/.myfiles installed (or before install completes), the file-test guard prevents a failure during shell startup.

Related to tamakiii/meta#276

🤖 Generated with Claude Code

[tamakiii-claude]

One-line companion to tamakiii/myfiles#219 (now merged), exactly as specified in tamakiii/meta#276. The [[ -f ~/.myfiles/shell/claude.zsh ]] guard prevents .zshrc startup failures on hosts where the myfiles half hasn't installed yet, which matches the same defensive posture as the launcher's missing-path filtering. Body references both #276 (issue) and #219 (sibling PR) with markdown links and uses Related to per the manual-closure convention. Pre-existing modifications elsewhere in the dotfiles working tree were correctly left unstaged. Approving.