docs: Add claude PATH troubleshooting section

[petebytes]

Summary

• Adds troubleshooting section for "claude not found" error when using uvx
• Documents PATH-based solution for subprocess environments that don't inherit shell aliases
• Includes alternative solutions for permanent PATH setup and symlinks

Problem

Users with Claude installed were encountering ⚠️ claude not found errors when running:

uvx --from git+https://github.com/github/spec-kit.git specify init --here

This occurs because uvx creates subprocess environments that don't inherit shell aliases, and claude is often installed in non-standard PATH locations.

Solution

Added concise troubleshooting section with:

• Quick fix using PATH prefix
• Alternative solutions for permanent setup
• Clear indication this applies when Claude is installed but not found

Testing

All documented solutions were tested and verified to work correctly.

[Copilot]

Pull Request Overview

This PR adds a troubleshooting section to help users resolve "claude not found" errors when using uvx to run spec-kit commands. The issue occurs when Claude is installed but uvx subprocess environments don't inherit shell aliases or PATH configurations.

• Adds dedicated troubleshooting section for Claude CLI PATH issues
• Provides quick fix using PATH prefix and alternative permanent solutions
• Documents the root cause as subprocess environments not inheriting shell configuration

---

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[Copilot]

The PATH assumes Claude is installed in $HOME/.claude/local, but this may not be accurate for all installations. Consider using a more generic example like PATH="/path/to/claude/directory:$PATH" or mention that users should replace with their actual Claude installation path.

Suggested change

	PATH="$HOME/.claude/local:$PATH" uvx --from git+https://github.com/github/spec-kit.git specify init --here
	# Replace /path/to/claude/directory with the actual path to your Claude installation
	PATH="/path/to/claude/directory:$PATH" uvx --from git+https://github.com/github/spec-kit.git specify init --here

[Copilot]

Similar to the quick fix, this assumes a specific installation path. Consider clarifying that users should verify their actual Claude installation location first, or provide instructions on how to find it.

Suggested change

	**Quick fix:**
	```bash
	PATH="$HOME/.claude/local:$PATH" uvx --from git+https://github.com/github/spec-kit.git specify init --here
	```
	**Other solutions:**
	- Find claude location: `which claude`
	- Add to shell permanently: `export PATH="$HOME/.claude/local:$PATH"` in `~/.bashrc`/`~/.zshrc`
	- Create symlink: `ln -s ~/.claude/local/claude /usr/local/bin/claude`
	**Quick fix (default path):**
	> Note: The path `$HOME/.claude/local` is the default for some installations. Your Claude installation may be elsewhere.
	> To find the actual location, run:
	>
	> ```bash
	> which claude
	> ```
	>
	> Then, update your PATH accordingly. For example, if `which claude` returns `/home/user/.claude/local/claude`, use:
	>
	> ```bash
	> export PATH="/home/user/.claude/local:$PATH"
	> ```
	>
	> You can run the initialization command after updating your PATH:
	>
	> ```bash
	> uvx --from git+https://github.com/github/spec-kit.git specify init --here
	> ```
	**Other solutions:**
	- Add to shell permanently: Add the export line above to your `~/.bashrc` or `~/.zshrc`
	- Create symlink: `ln -s $(which claude) /usr/local/bin/claude`

[localden]

@petebytes should we make this a bit more generic for other CLI tools as well?