Prepare project for pipeline takeover: task tracker, UX doc, CLAUDE.md pointers

Adds docs/tasks/ (16 epics + 102 stories converted to task/subtask files with
statuses.md as the new status source of truth) and docs/ux-design.md
(retrospective design-system reference), and points CLAUDE.md at them.
docs/prd.md and docs/architecture.md are kept as BMAD wrote them; the legacy
docs/stories/, docs/epics/, docs/qa/gates/ and .bmad-core/ stay in place as
historical/traceability records, superseded but not deleted.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/tasks/13-3.md

@@ -0,0 +1,20 @@
+---
+id: 13-3
+title: 13-3 Subtle Background Pattern Implementation
+status: QA Review
+date: 2026-09-27
+parent: 13
+---
+
+## Description
+
+As a visitor to the authentication pages I want to see a subtle, elegant background pattern on the form side So that the page feels polished and professionally designed. **Option A: Geometric (Recommended)** - Simple diagonal lines or dots - Clean, modern aesthetic - Easier to create and maintain. Full implementation history: docs/stories/story-13.3-background-pattern.md
+
+## Acceptance Criteria
+
+- [ ] AC1: Create SVG Pattern Asset: Given the need for a subtle background pattern; When the pattern is created; Then :
+- [ ] AC2: Pattern Placement: Given the SVG pattern is created; When applied to the auth layout; Then :
+- [ ] AC3: Pattern Opacity: Given readability requirements; When the pattern is displayed; Then :
+- [ ] AC4: CSS Implementation: Given the pattern asset; When integrated into CSS; Then :
+- [ ] AC5: Performance Consideration: Given page load performance; When the pattern loads; Then :
+- [ ] AC6: Mobile Compatibility: Given mobile viewport; When pattern is displayed; Then :