build: drop the local Python release method, return to CI-only installer builds

Removes the single-command Python packaging method (build/make_release.py
+ build/build_portable_zip.py + build/macos/build_zip.sh) and the portable
.zip artifacts it produced. Release builds go back to the original GitHub
Actions process: the CI matrix builds one installer per platform (.dmg /
.exe / .AppImage) on tag push and attaches them to a GitHub Release.

Tesseract OCR bundling is preserved: the fetch helpers the workflow depends
on (fetch_tessdata, fetch_tesseract_for_platform) are extracted into a
standalone build/tesseract.py, which build.yml now imports.

Docs (README, build/README, DEVELOPER, TECHNICAL, USER-GUIDE, vendor README,
es translations) updated to drop the portable-zip flavor and point at the
new module.

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

build/vendor/README.md

@@ -4,9 +4,10 @@ This tree holds the third-party assets that get bundled into the
 PyInstaller artifacts but that we deliberately do **not** keep in git
 (too large / license-encumbered / re-fetchable on demand).
 
-The build pipeline (`build/make_release.py`) populates everything in
-here before the PyInstaller step. The contents are git-ignored except
-for this README.
+The build's Tesseract helper (`build/tesseract.py`) populates
+everything in here before the PyInstaller step — CI
+(`.github/workflows/build.yml`) calls it ahead of the build. The
+contents are git-ignored except for this README.
 
 ## tessdata/
 
@@ -40,9 +41,9 @@ statements (the only OCR use case so far), the extra accuracy of the
 
 ### How it gets populated
 
-`build/make_release.py::fetch_tessdata()` checks for
+`build/tesseract.py::fetch_tessdata()` checks for
 `build/vendor/tessdata/eng.traineddata` on every run. If it's
-missing, the script downloads it from the canonical URL above and
+missing, it downloads the file from the canonical URL above and
 caches it here. Subsequent builds reuse the cached file.
 
 On CI, the directory is restored from the GitHub Actions cache so we