feat: add claude wrapper that auto-links AGENTS.md as CLAUDE.md

New functions/claude.fish wraps the claude CLI. Before launch it checks the
current directory and the git project root; when CLAUDE.md is absent but
AGENTS.md is present, it creates a relative symlink CLAUDE.md -> AGENTS.md so
Claude Code picks up shared agent instructions without duplicating the file.
Arguments are forwarded verbatim.

Implemented as a C1 command shadow: when __fish_config_op_aliases (or the
master __fish_config_opinionated) is disabled, the call passes through to the
bare claude binary unchanged. Link-creation notices print to stderr in green.

Documents the new shadow in docs/fish-config.md (section 5.12 AI tools, C1
component reference table, and C1 summary list) and adds a claude-cli anchor
to docs/fish-config.index.

docs/fish-config.index

@@ -130,6 +130,7 @@ logs=### logs
 smart-exit=### smart_exit
 ai=## 5.12 AI and Developer Tools
 antigravity=### antigravity
+claude-cli=### claude
 claude=### claude-resume
 claude-docs=### claude-docs
 claude-pr=### claude-pr