docs(arch): end-to-end system + tech-stack diagrams

New ARCHITECTURE.md pulls the desktop app (TECHNICAL.md) and the
license server (LICENSE-SERVER.md) into a single picture — the two
were never reconciled into an end-to-end view before.

Contents:
  §1. System diagram (ASCII) showing operator laptop, license
      server stack (nginx → FastAPI → Postgres), Postmark, Gumroad,
      and the buyer's machine — with the three primary flows
      (sale, manual mint, offline activation) traced through it.
  §2. Tech stack diagram, layered: desktop / server / operator /
      external SaaS, with version pins.
  §3. Trust + isolation boundaries table — what crosses each one
      and what the threat model is.
  §4. "Where things are stored" — paths, tables, files.
  §5. Pointers to the deeper per-component docs.

ASCII over Mermaid since the repo's Gitea version is unknown and
plain text renders in every viewer / IDE / raw `cat`.

LICENSE-SERVER.md status flipped from "design proposal, not built"
to "deployed (PR 1 + PR 2 code merged)" — that was stale since
the PR 1 deploy yesterday.

TECHNICAL.md and ADMIN.md gain one-line pointers to ARCHITECTURE.md
so people land at the unified view when looking for "how does it
all fit together".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/TECHNICAL.md

@@ -3,6 +3,9 @@
 > Creator-only. Do not ship to buyers.
 > **Version**: 1.6 · **Updated**: 2026-05-01
 
+For the end-to-end picture (desktop app + license server + storefronts
++ email), see `ARCHITECTURE.md`. This doc focuses on desktop internals.
+
 ## 1. Architecture
 
 - **Dual interface**: CLI + GUI, both wrapping the same `src/core/` library.