Fix YAML parse error in mean-reversion-strategy notebooks

[Copilot]

CI was failing with YAMLException: unknown escape sequence when Quarto parsed fig-cap cell directives in the mean-reversion-strategy notebook series. YAML double-quoted strings interpret \ as an escape character, making LaTeX sequences like \sqrt, \theta, \sigma, \mathrm invalid.

Changes

• posts/mean-reversion-strategy-2/index.ipynb — converted fig-cap values from double-quoted to single-quoted YAML strings in cells 7, 10, 11, 12
• posts/mean-reversion-strategy-3/index.ipynb — converted fig-cap values from double-quoted to single-quoted YAML strings in cells 3, 6, 7, 8
• posts/mean-reversion-strategy-4/index.ipynb — converted fig-cap values from double-quoted to single-quoted YAML strings in cells 3, 5, 8, 10

Single-quoted YAML strings treat backslashes literally, allowing LaTeX math to pass through correctly.

-#| fig-cap: "The standard deviation of $Y_T$ matches the closed-form $\sqrt{M^2 s_T^2 + s_T^4/2}$."
+#| fig-cap: 'The standard deviation of $Y_T$ matches the closed-form $\sqrt{M^2 s_T^2 + s_T^4/2}$.'

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.

[steveya]

CI failed again @copilot

[Copilot]

CI failed again @copilot

The same YAML backslash issue existed in mean-reversion-strategy-3 (4 cells) and mean-reversion-strategy-4 (4 cells) as well. Fixed all of them in 4565bc3 — converted remaining double-quoted fig-cap strings with LaTeX backslash sequences to single-quoted strings across all notebooks in the series.