Replace PDF Expert?

Build a personal replacement for PDF Expert in an empty repository.
Use Next.js 15, TypeScript, Python 3.12, FastAPI, pikepdf, LibreOffice headless, and PostgreSQL; do not offer alternative stacks.
The core loop is: annotate, fill, merge, and lightly edit PDFs in a local desktop app, preserve originals, generate auditable outputs, and keep files in a user-owned store.
Make the first run work locally with one documented command.
Store all user data locally by default and make export straightforward.
Put secrets in .env, ship .env.example, and never commit credentials.
Keep every original immutable and write each operation to a versioned output file.
Support merge, split, reorder, rotate, compress, watermark, redact, OCR, and Office-to-PDF conversion.
Render page previews and warn when fonts, forms, signatures, or encryption may be altered.
For signature mode, place fields, invite signers, record consent, and seal a final PDF hash.
Maintain an append-only event log with timestamps, document hashes, and delivery outcomes.
Add file expiry, download, deletion, backup, and a prominent low-stakes-use warning.
Include clear empty, loading, success, and recoverable error states.
Add input validation, safe filenames, and graceful handling of unavailable APIs.
Write focused tests for the core transformation and one end-to-end happy path.
Create a README with setup, architecture, permissions, data location, and backup steps.
Do not add accounts, billing, telemetry, analytics, or a hosted control plane.
Deliberately leave out qualified or regulated electronic signatures.
Deliberately leave out government identity verification.
Deliberately leave out full Acrobat-level editing and enterprise document governance.
Finish by running the tests and listing the exact commands used.