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>

docs/TECHNICAL.md

@@ -124,7 +124,7 @@ Tag a release → 3 platform artifacts upload to GitHub Releases. Manual: copy t
 
 ### 3.10 Bundled Tesseract (PDF Extractor OCR)
 
-Frozen builds ship Tesseract 5.5 + `eng.traineddata` inside the PyInstaller bundle so scanned PDFs work without a separate install. Per-platform binary URLs pinned in `build/make_release.py`; tessdata vendored at `build/vendor/tessdata/eng.traineddata`. License attribution in `LICENSE_TESSERACT.txt` at the repo root.
+Frozen builds ship Tesseract 5.5 + `eng.traineddata` inside the PyInstaller bundle so scanned PDFs work without a separate install. Per-platform binary URLs pinned in `build/tesseract.py`; tessdata vendored at `build/vendor/tessdata/eng.traineddata`. License attribution in `LICENSE_TESSERACT.txt` at the repo root.
 
 **Discovery order at runtime** (see `docs/DEVELOPER.md` for the full Path layout):