Footnotes in self-care chapter should be reformatted #262

Footnotes in the self-care chapter are throwing build warnings:

WARNING: 'myst' cross-reference target not found: 'user-content-fn-1' [myst.xref_missing]

Root cause: The source uses [^1] footnote syntax, which MyST renders with user-content-fn-* IDs (a GitBook convention that MyST's markdown-it parser preserves). However, Sphinx's cross-reference resolver does not register these IDs as valid targets, so it reports them as missing.

The footnotes render correctly in the HTML output — the references and back-references work. The warnings are false positives from MyST's cross-reference validation, but they clutter the build log and may mask real issues.

Fix (options):

1. Add user-content-fn-* patterns to myst_xref_missing suppression in conf.py:

   myst_xref_missing_suppress = [r"user-content-fn-\d+"]

2. Configure MyST to use Sphinx-native footnote IDs instead of GitBook-style IDs
3. Suppress the specific warning type in conf.py:

   suppress_warnings = ["myst.xref_missing"]

(Reported by @sanchuanhehe in theopensourceway/production#6)