Add per-variable exploratory analysis for ds4owd-002 registrations

[larnsce]

Summary

Adds analysis.qmd alongside the existing narrative index.qmd in pages/blog/posts/2025-09-01-ds4owd-002-registration-analysis/. It walks through every registration survey variable with a brief summary, a frequency plot, and two observations plus one course implication per plot.

The document is draft: true pending review.

Closes #134

What's included

• analysis.qmd covering all ~54 survey questions across nine thematic sections (identity, demographics, barriers, programming, version control, tooling, LLM/AI, digital habits, goals and consent)
• Reusable plot_freq and plot_multi helpers that join the choices dictionary for human-readable labels
• Free-text and consent fields summarised by completeness rather than plotted
• Committed _freeze output (26 figures + execute-results) so the page builds without re-running R
• prompt-history.md per the repository Session Standards

Notes

• raw_data.csv is gitignored (pre-existing working-tree change, not part of this PR), so the page relies on the committed _freeze output to build on a clean checkout.
• The .gitignore and index.qmd working-tree changes were left out of this feature and are tracked separately.

Test plan

• quarto render pages/blog/posts/2025-09-01-ds4owd-002-registration-analysis/analysis.qmd builds cleanly
• Each section's observations match its plot
• Front matter (title, author, date, categories) is correct
• Decide whether to keep draft: true or publish