Refactor SQLite transactions, settings, and web reader

[dowellhz]

What changed

• Added a shared checked SQLite transaction executor and migrated word records, PDF embeddings, and personal vocabulary writes.
• Split AI settings construction into focused General and Model builders, and separated speech runtime downloads/diagnostics from speech selection logic.
• Split the Web Reader entry script into focused TTS and selection modules while preserving the existing WebKit bridge API.
• Updated regression tests and architecture/code-map documentation.

Why

Several files were at or near the repository's 500-line limit and combined unrelated responsibilities. SQLite transaction handling was also duplicated across stores, which allowed PersonalVocabularyProfileStore to return success without checking whether COMMIT succeeded.

Impact

There should be no user-visible behavior change. The new boundaries make transaction failure handling consistent, reduce controller and JavaScript module size, and make future changes easier to test without exceeding the line limit.

Validation

• ./tests/run.sh — all 144 logic tests passed
• ./scripts/check.sh --no-build — passed
• ./scripts/check_ui_theme.sh --warnings-as-errors — passed
• ./scripts/build_app.sh — debug arm64 build and signing passed
• git diff --check — passed