feat(bookimporter): switch Windows CI packaging to portable ZIP output

[arieldaniely]

Motivation

• CI and the project currently produce a Windows installer EXE for the Book Importer, but a portable (no-install) distribution is preferable for users who want a self-contained executable folder.
• The goal is to change the automated build and packaging flow so CI emits a portable ZIP containing the Compose app folder instead of an installer.

Description

• Added a new Gradle distribution task :bookimporter:packageWindowsPortable that zips the release app folder into SeforimBookImporter-windows-portable.zip (file: generator/bookimporter/build.gradle.kts).
• Added a root-level convenience task packageBookImporterWindowsPortable that depends on the module task so repository-level invocations can produce the portable ZIP (file: build.gradle.kts).
• Replaced the Windows installer CI workflow with a new workflow that runs packageBookImporterWindowsPortable and uploads the produced portable ZIP artifact (renamed workflow file to .github/workflows/build-bookimporter-portable.yml).
• Updated generator/bookimporter/README.md to document the portable ZIP workflow and how to run the app from the extracted folder.

Testing

• Ran ./gradlew :bookimporter:tasks --all --no-daemon to verify the new tasks are registered and visible, which completed successfully.
• Executed ./gradlew :bookimporter:packageWindowsPortable -m --no-daemon to perform a dry-run packaging build which completed successfully (tasks were configured and the package task was exercised/skipped as expected in a matrixed invocation).
• No DB schema or runtime API changes were introduced by this packaging change.

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Codex Task