Simplify curl installer usage and strengthen bash PATH setup

[sawrus]

Summary

• make GitHub release downloads default to sawrus/code-obfuscator so users can run installer via curl ... | bash without extra env vars
• update installer shell detection fallback to bash
• for bash users, append PATH export to both ~/.bashrc and ~/.bash_profile to cover interactive and login shells
• update README and docs one-liner examples to remove CODE_OBFUSCATOR_INSTALL_REPO=...

Why

Users should be able to install with the shortest possible command:

curl -fsSL https://raw.githubusercontent.com/sawrus/code-obfuscator/main/install | bash

And have code-obfuscator immediately available after reloading/opening a bash shell.

Notes

• no runtime tests were executed in this pass (static/script-doc update only)

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Codex Task