Documentation conventions: no em-dash, uv/ppp/tcl examples, a house style note #77

The maintainer's instructions (2026-10-03, relayed by the ecosystem lead): (1) no em-dash anywhere in documents or code, as an AGENTS rule; (2) install and run examples use only uv, ppp and tcl, never pip, as an AGENTS rule (the 0.1.0a1 Release notes stay as a record); (3) this repository's guide is the reference for every repository's documentation, so its style is written down as a house style note other repositories follow. Done when git grep finds no em-dash, every install/run example uses uv/ppp/tcl, AGENTS.md section 17 carries both rules and points at docs/style/writing.md, and check_guide reports 0 findings.