docs: pivot to desktop-first PDF review — add architecture package and deprecate EDMS blueprint

[gitgrahamdunn]

Motivation

• Pivot the product from a web/Git-style EDMS to a desktop-first, local-first engineering PDF review tool optimized for large PDFs and traceable review workflows.
• Establish a long-term renderer abstraction so PDF.js can be used for v1 while enabling a native renderer sidecar later without rewriting domain logic.
• Provide a concrete, production-oriented architecture, repo-refactor plan, and phased roadmap so implementation can begin with clear boundaries and contracts.

Description

• Added docs/PDF_REVIEW_ARCHITECTURE_PACKAGE.md, a comprehensive architecture package that includes an executive summary, architecture blueprint, renderer abstraction contract, large-PDF performance strategy, domain model, data flows, repo refactor plan, phased roadmap, and recommended immediate next coding step.
• Replaced the prior docs/EDMS_BLUEPRINT.md content with a short deprecation notice that points consumers to the new desktop-first architecture document.
• Bundled these documentation updates into this PR so the new architecture becomes the canonical source of truth for the pivot and the repo layout/contract work can begin.

Testing

• Ran repository integrity and diff checks to validate the new/updated files are syntactically consistent with project docs and the repo state, and those checks passed.
• Verified the new architecture document file is present and readable in the docs tree and the deprecated blueprint now contains the deprecation notice.
• No runtime or unit tests were applicable because this is a docs-only change; no code paths were modified.

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Codex Task