Build strict: enable -W in ci.yml and publish.yml

Both builds carried `# TODO: Re-enable -W flag once all lectures are
translated and warnings are resolved`. The precondition is already met:
this edition has 26 of 26 lectures with a `_toc.yml` identical to
source, so there are no untranslated lectures left to produce dangling
cross-references.

The case for strict is stronger than build hygiene. A translated
edition carries the same code as its English source, so a warning here
that does not appear upstream is evidence of a translation defect, not
noise — which makes -W a translation-quality signal.

It is also the last line of defence against a class of silent engine
corruption. QuantEcon/action-translation#118 (a resync wrapped an
entire 1,465-line document in a code fence and mis-derived its title
from a Python tuple-unpacking line) and #119 (a `{raw} jupyter`
directive argument stripped to `{raw}`) both reported success at run
time, looked plausible in review, and surfaced weeks later only
because a downstream repo built with -n -W. Without the flag this
edition would merge that class of damage green.

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

Author: mmcky

.github/workflows/ci.yml

@@ -42,8 +42,7 @@ jobs:
       - name: Build HTML
         shell: bash -l {0}
         run: |
-          jb build lectures --path-output ./ -n --keep-going
-          # TODO: Re-enable -W flag once all lectures are translated and warnings are resolved
+          jb build lectures --path-output ./ -n -W --keep-going
       - name: Upload Execution Reports
         uses: actions/upload-artifact@v7
         if: failure()

.github/workflows/publish.yml

@@ -56,8 +56,7 @@ jobs:
       - name: Build HTML
         shell: bash -l {0}
         run: |
-          jb build lectures --path-output ./ -n --keep-going
-          # TODO: Re-enable -W flag once all lectures are translated and warnings are resolved
+          jb build lectures --path-output ./ -n -W --keep-going
       # Serves at the default Pages URL (no cname):
       # https://quantecon.github.io/lecture-python-programming.fr/
       - name: Deploy to GitHub Pages