docs: Audit and document admin UI architecture (Ticket 6.1)

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Overview

Adds a comprehensive architecture document at docs/admin-ui-architecture.md and a rendered architecture diagram at docs/admin-ui-architecture-diagram.png that audit the current Open Admin Platform front-end. This is a documentation-only change — no source code was modified. The document is intended to guide future admin UI rewrite efforts.

Label: Enhancement
Status: ready-for-code-review

What's Documented

• JavaScript inventory — All 96 JS files in the admin directory cataloged with line counts, purposes, and dependencies. Organized by layer (core, UI, component, vendor, plugins).
• BLCAdmin namespace API — Modal stack management, handler registration pipeline (pre-validation → validation → post-validation → post-submit), field initialization flow, selectize/redactor integration, event system.
• jQuery plugins & libraries — Foundation 3 (12 component plugins), Redactor (6 custom plugins), Selectize, DataTables 1.13.1, jQuery UI 1.13.3, Spectrum, QueryBuilder, Bloodhound/Typeahead, Moment.js, and others. Notes the two identical copies of jQuery 3.5.1.
• Thymeleaf template map — 120 templates documented with hierarchy (layout → views → components → fields), including 50+ field type templates (edit + filter variants).
• AJAX endpoints — AdminBasicEntityController endpoint table with HTTP methods, return types, and purpose. Request/response flow diagrams for page loads, modal workflows, and collection fetches.
• Critical features — Entity CRUD, ListGrid (pagination/filter/sort), Rule Builder, Filter Builder, Asset Management, Translations, Session Management — each mapped to supporting JS files, templates, and controllers.
• Risks & tech debt — Flags: no module system, EOL Foundation 3, dual jQuery copies, Bootstrap 2 + Foundation 3 coexistence, no JS tests, no build pipeline.
• Framework replacement recommendations — Evaluates React (primary) and Vue (alternative) with a 4-phase migration strategy and library replacement matrix.

Architecture Diagram

A rendered PNG architecture diagram is included (docs/admin-ui-architecture-diagram.png) showing the four-layer stack: Browser (vendor libraries) → BLCAdmin Namespace (application JS) → Spring MVC Server (controllers + Thymeleaf) → Open Admin Platform (metadata engine). A collapsible ASCII-art fallback is also embedded in the markdown.

Items for Reviewer Attention

1. Accuracy of file inventories — Line counts and file purposes were derived from source code reading. Spot-check a few entries against the actual files in admin/broadleaf-open-admin-platform/src/main/resources/open_admin_style/js/admin/ to verify.
2. Framework recommendation (Section 14) — Recommends React+TypeScript as the primary replacement. This is opinionated — confirm alignment with team direction.
3. PNG diagram rendering — Verify the architecture diagram PNG displays correctly on GitHub. A text fallback is provided in a <details> block.
4. Template counts — Document claims 120 Thymeleaf templates and 50 field-type templates. Verify these numbers are reasonable against the actual template directories.

Human Review Checklist

• Spot-check 3–5 JS file entries (line counts, described purpose) against actual source
• Verify PNG diagram renders on GitHub and is readable
• Confirm framework recommendation (React vs Vue) aligns with team direction
• Review risks/tech-debt section for completeness — any major items missing?

Link to Devin session: https://app.devin.ai/sessions/4aad79b8bbc6481b988a6d49ef53ca5b
Requested by: @Colhodm

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✅ Devin Review: No Issues Found

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