Bump install.sh / install.ps1 pin to unsloth>=2026.8.6, unsloth-zoo>=2026.8.5

[danielhanchen]

Summary

• PyPI release unsloth 2026.8.6 is now live.
• Bumps the pinned floor in install.sh and install.ps1 from unsloth>=2026.8.5 to unsloth>=2026.8.6 so fresh installs resolve to the new wheel.
• Bumps the companion unsloth-zoo floor from unsloth-zoo>=2026.8.4 to unsloth-zoo>=2026.8.5 on the same lines, matching the unsloth_zoo>=2026.8.5 floor already declared in pyproject.toml.
• Updates all 5 install commands in each of install.sh and install.ps1 (migrated no-torch / migrated / no-torch / local / auto torch backend paths).
• Tagged on main as v0.1.523-beta.

Follows the same pattern as #5716, and the explicit-zoo-floor approach from #6440.

Scope

• Only the 5 base-install specs in each script change.
• The --reinstall-package / --upgrade-package flags and the unsloth-zoo @ git+https://... git-main overlay lines are untouched.

Checks

• bash -n install.sh passes.
• install.ps1 parses with 0 syntax errors via [System.Management.Automation.Language.Parser]::ParseFile.
• No stale unsloth>=2026.8.5 or unsloth-zoo>=2026.8.4 specs remain in either script.

Test plan

• Sanity-run install.sh on a clean Linux host
• Sanity-run install.ps1 on a clean Windows host
• Confirm uv pip install "unsloth>=2026.8.6" "unsloth-zoo>=2026.8.5" resolves cleanly