fix(docs): bump mkdocs-material so pymdown-extensions 11 resolves - #672

What

Bumps mkdocs-material from 9.6.18 to 9.7.7 in docs/requirements.txt. One line; pymdown-extensions stays at 11.0.1.

Why

#650 bumped pymdown-extensions to 11.0.1, but mkdocs-material==9.6.18 declares:

Requires-Dist: pymdown-extensions~=10.2

~=10.2 means >=10.2,<11, so pip has two rules it cannot both satisfy and aborts before rendering anything:

ERROR: Cannot install -r docs/requirements.txt (line 13) and pymdown-extensions==11.0.1
because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested pymdown-extensions==11.0.1
    mkdocs-material 9.6.18 depends on pymdown-extensions~=10.2
ERROR: ResolutionImpossible

This breaks Docs PR Preview on every open PR, and main's own docs build — the Install docs requirements step never completes.

mkdocs-material 9.7.0 is the first release to relax the ceiling to pymdown-extensions>=10.2; 9.6.20, the last 9.6.x, still pins ~=10.2. So no patch-level bump escapes this — the only ways out are downgrading pymdown-extensions below 11 or moving mkdocs-material to >= 9.7.0.