[DO NOT MERGE] Integration: high priority - #245

The sphinx job unconditionally ran (and tried to publish to gh-pages)
on every PR, including ones whose branch lives in a fork -- even the
author's own fork (e.g. #198). GitHub Actions always issues a
read-only GITHUB_TOKEN for pull_request-triggered runs when the head
repo differs from the base repo, so the gh-pages push step there fails
by design, regardless of repo/workflow permission settings.

There was already a commented-out attempt at this exact guard inside
sphinx.yml itself (`if: github.event_name != 'pull_request'`), but it
could never have worked there: sphinx.yml is invoked via
`workflow_call`, and github.event_name inside a called workflow is
always "workflow_call", never the original triggering event. Moving
the condition to the caller job in master.yml (which does see the real
triggering event) is what actually works -- removed the dead comment
from sphinx.yml accordingly.

This also means PR runs no longer spend ~10+ minutes building docs
that were never going anywhere, and unreviewed PR content never
reaches the live public docs site.

Project principal-point displacement onto the common normal of unit
directions, with a scalar perpendicular-distance fallback for parallel
lines. Cover intersecting, coincident and skew lines, direction rescaling,
operand reversal and the parallel tolerance.

AI assistance: prepared with Codex; validation executed locally.

Python 3.10 imports Self from typing_extensions. Require the first release that provides it so dependency resolution cannot silently install an incompatible older version.

Assisted-by: OpenAI Codex
Signed-off-by: 李永祺 <doribelove@gmail.com>

… push

…honormality

…3.10