Two minor source defects surfaced during zh-cn resync review (ols, cass_fiscal)

While resyncing the Chinese edition (lecture-python.zh-cn) against current main (c0146d3), two small defects in the English source were noticed. Neither breaks the build; filing so they can be cleaned up at the source (the fixes then propagate to every translated edition automatically).

1. lectures/ols.md:226 — stray full stop splits a sentence. The bullet reads "The positive $\hat{\beta}_1$ parameter estimate implies that." and then continues on the next line with a lowercase "institutional quality has a positive effect on economic outcomes…". The full stop after "that" is spurious — it renders as two broken fragments. Fix: delete the . so lines 226–227 read as one sentence. (The zh translation already reads it as a single sentence, which is how it was caught.)

2. lectures/cass_fiscal.md:182 — misspelled equation label (eq:constrant_house). "constrant" should be "constraint". The label is defined but never referenced anywhere in the corpus (grep finds only the definition), so this is cosmetic — no broken cross-reference — but worth correcting for cleanliness. If corrected, only the definition needs changing since nothing references it.

Both were verified present on main at c0146d3 on 2026-07-19.

Inspect the two named source locations, lectures/ols.md:226 and lectures/cass_fiscal.md:182, and compare the surrounding prose and equation label with the issue description. Confirm the misspelled label has no references, then verify the sentence reads continuously and the label is spelled consistently in the source.