FIX: execution and doc failures from the Anaconda 2026.07 cache build (#183)

Resolves the four failures reported in #182. All four are target-side
defects; the English source is healthy in every case.

likelihood_bayes — the font block called `mpl.font_manager.fontManager`
and `plt.rcParams` before `import matplotlib.pyplot as plt`. Newer
matplotlib no longer imports `font_manager` as a side effect of
`import matplotlib`, so this raised AttributeError (and would have
raised NameError on `plt`). Moved the pyplot import above both uses.
An audit of the font block across all 69 lectures found this the only
file with either ordering hazard.

kalman_2 — a `.text()` annotation drew the covariance matrix with
`\begin{bmatrix}`, which matplotlib mathtext cannot render (it supports
no LaTeX environments). Rewritten as `\left[ \substack{...} \right]`,
which renders an equivalent bracketed 2x2 matrix under mathtext, using
`\;` as the column separator rather than `&`. This keeps the
drop-usetex standard from #22 intact with no loss of information.
The lecture's other `\begin{bmatrix}` uses are inside `{math}` blocks,
rendered by MathJax, and are unaffected.

sir_model — the header directive had lost its argument: `{raw}` instead
of `{raw} jupyter`. The other 50 lectures carrying this directive kept
theirs.

ak_aiyagari — the file carried a stray fence at line 38 followed by a
duplicated copy of the original frontmatter, and a doubled closing
fence at EOF. The stray opener ran to line 56, swallowing both the H1
title and the `_admonition/gpu.md` include, which is what produced the
13 "headings start at H2" warnings. Removed both strays; the file's
fence structure now matches the English source exactly (122). The
`translation.title` field was also corrupt ("V, σ, μ") and has been set
to the lecture title. An edition-wide sweep found no other file with
unbalanced fences.

The last two are content corruption introduced in translation and
warrant engine issues against action-translation; they are not covered
by the existing #107/#115/#116/#117 set.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: mmcky

lectures/ak_aiyagari.md

@@ -10,7 +10,7 @@ kernelspec:
   language: python
   name: python3
 translation:
-  title: V, σ, μ
+  title: 长寿、异质性个体、世代交叠模型
   headings:
     Overview: 概述
     Environment: 经济环境
@@ -35,21 +35,6 @@ translation:
     'Experiment 2: Preannounced tax cut': 实验2：预先宣布的减税
 ---
 
-```
----
-jupytext:
-  text_representation:
-    extension: .md
-    format_name: myst
-    format_version: 0.13
-    jupytext_version: 1.17.3
-kernelspec:
-  display_name: Python 3 (ipykernel)
-  language: python
-  name: python3
----
-
-
 # 长寿、异质性个体、世代交叠模型
 
 ```{include} _admonition/gpu.md
@@ -1477,4 +1462,3 @@ ax2.set_ylabel(r"j")
 
 plt.show()
 ```
-```

lectures/kalman_2.md

@@ -352,8 +352,8 @@ for i, t in enumerate(np.linspace(0, T-1, 3, dtype=int)):
     axs[i].set_ylabel(r'$u_{{{}}}$'.format(str(t)))
     
     cov_latex = (
-        r'$\Sigma_{{{}}}= \begin{{bmatrix}} {:.2f} & {:.2f} \\ '
-        r'{:.2f} & {:.2f} \end{{bmatrix}}$'
+        r'$\Sigma_{{{}}}= \left[ \substack{{{:.2f} \; {:.2f} \\ '
+        r'{:.2f} \; {:.2f}}} \right]$'
     ).format(t, cov[0, 0], cov[0, 1], cov[1, 0], cov[1, 1])
     axs[i].text(0.33, -0.15, cov_latex, transform=axs[i].transAxes)
 

lectures/likelihood_bayes.md

@@ -62,10 +62,10 @@ translation:
 
 FONTPATH = "fonts/SourceHanSerifSC-SemiBold.otf"
 import matplotlib as mpl
+import matplotlib.pyplot as plt
 mpl.font_manager.fontManager.addfont(FONTPATH)
 plt.rcParams['font.family'] = ['Source Han Serif SC']
 
-import matplotlib.pyplot as plt
 import numpy as np
 from numba import vectorize, jit, prange
 from math import gamma

lectures/sir_model.md

@@ -21,7 +21,7 @@ translation:
     Ending Lockdown: 解除封锁
 ---
 
-```{raw}
+```{raw} jupyter
 <div id="qe-notebook-header" align="right" style="text-align:right;">
         <a href="https://quantecon.org/" title="quantecon.org">
                 <img style="width:250px;display:inline;" width="250px" src="https://assets.quantecon.org/img/qe-menubar-logo.svg" alt="QuantEcon">