Doc Revision: Quickstart Manual Install broken

[KenOcheltree]

Summary of Requested Changes:
https://agentstack.beeai.dev/stable/introduction/quickstart

Change all references in the manual installation instructions to python 3.13 to 3.14 to allow version 0.7.1 to install. If python 3.13 is used, version 0.6.2 installs in error

Requirements
Undate the two instances of 3.13 to 3.14.

Task Checklist

• Contributing Guideline Compliance: I read and complied by "Documentation Contribution Guidelines" section of the Agent Stack project CONTRIBUTING.md guide.
• Snippet Test: Verified all code works in a fresh environment (fresh agent stack install and clean environment).
• Visual Preview: Checked formatting/layout via Mintlify.
• CLI Sync: Ran mise run agentstack-cli:docs (if applicable).
• [] Location: Updates placed in docs/development for go live during next release or both docs/development and docs/stable for urgent go live.