Switch Vale to the upstream ai-tells package

[adamtheturtle]

What changed

• Replace the single-rule ClearProse package with tbhb/vale-ai-tells v1.29.0.
• Keep all compatible ai-tells rules enabled.
• Disable only rules that flag established technical, example, or release-note prose already present in this repository.
• Update the Vale workflow/hook comment where one names the old package.

Why

The upstream package covers em dashes as well as a much broader set of patterns associated with AI-written prose. Repository-specific exceptions avoid rewriting valid technical terminology and reference material merely to satisfy a general-audience heuristic.

Validation

• uvx --with docutils vale@3.13.0.0 over every tracked *.rst and *.md file
• Result: passed with zero errors