docs: add desktop-first architecture blueprint for Tauri pivot

[gitgrahamdunn]

Motivation

• Pivot the product to a desktop-first architecture for PDF markup, review, and squad-check workflows, prioritizing local-first persistence and offline-first UX.
• Provide a production-grade blueprint that centers Tauri + React + TypeScript + PDF.js with SQLite and local file storage as the system-of-record for structured markups and audit trails.
• Give a concrete migration/refactor path from the current browser-first repo layout to a unified desktop runtime to guide implementation and planning.

Description

• Add docs/DESKTOP_FIRST_ARCHITECTURE.md which defines core principles, runtime topology (Tauri Rust + React frontend + local storage), and modular boundaries for the product.
• Include a recommended repo layout for an integrated Tauri + React + SQLite + PDF.js app and a suggested packages/migrations/docs organization.
• Define the domain model for Project, Document, DocumentRevision, Markup, CommentThread, ReviewerAssignment, SquadCheck, Confirmation, Reminder, and AuditEvent.
• Document end-to-end data flows (open, render, create markup, attach comments, save, export) and provide a three-phase implementation roadmap plus a practical refactor strategy for this repo.

Testing

• This is a documentation-only change; no unit or integration tests were modified or required for this PR.
• Validation commands executed successfully: viewed the new file with nl/sed, confirmed repo status with git status --short, and committed the file with git commit (commit succeeded).

---

Codex Task

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
gitplant	Ready	Preview, Comment	Mar 9, 2026 2:51pm
gitplant-backend	Ready	Preview, Comment	Mar 9, 2026 2:51pm
gitplant-oggy	Ready	Preview, Comment	Mar 9, 2026 2:51pm