docs: Add missing architecture flow and update roadmap for dashboard/onboarding

Requirements:
- Add 6.4.3 Architecture Spike & Proposal Flow diagram
- Documents the flow from approved requirements → collaborative brainstorm →
  proposal → client approval → ADRs → sprint planning

Implementation Roadmap:
- Add Phase 1.5: Main Dashboard & Onboarding section
- Add issues #47-50 for main dashboard and project creation wizard
- Update progress summary (Phase 1 now at ~75%)
- Add blocking items for new design work

Related Issues:
- #47: [DESIGN] Main Dashboard / Projects List Page
- #48: Implement Main Dashboard / Projects List Page
- #49: [DESIGN] Project Creation Wizard
- #50: Implement Project Creation Wizard

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/requirements/SYNDARIX_REQUIREMENTS.md

@@ -1427,6 +1427,99 @@ def create_issue(
                       +----------+
 ```
 
+#### 6.4.3 Architecture Spike & Proposal Flow
+
+```
++----------+                           +----------+
+|Approved  |   1. Trigger Spike        |   PO     |
+|Require-  |-------------------------->|  Agent   |
+|ments     |                           +----------+
++----------+                                |
+                                       2. Summarize
+                                         Context
+                                            |
+                                            v
++----------+   3. Requirements    +---------------+
+|   BA     |<---------------------|  Spike Start  |
+|  Agent   |    Handoff           |   Workflow    |
++----------+                      +---------------+
+     |                                     |
+4. Deep                               5. Invite
+   Analysis                            Architect
+     |                                     |
+     v                                     v
++----------+                        +----------+
+|  Domain  |                        |Architect |
+|  Model   |                        |  Agent   |
++----------+                        +----------+
+     |                                     |
+     +---------------+---------------------+
+                     |
+              6. Collaborative
+                Brainstorm
+                     |
+                     v
+            +---------------+
+            | Tech Stack    |
+            | Discussion    |
+            +---------------+
+                     |
+              7. Generate
+                Proposal
+                     |
+                     v
+            +---------------+
+            | Architecture  |
+            | Proposal Doc  |
+            +---------------+
+                     |
+              8. Create ADRs
+                     |
+                     v
+            +---------------+
+            |    ADRs       |
+            | (Decisions)   |
+            +---------------+
+                     |
+              9. Present
+               to Client
+                     |
+                     v
++--------+    10. Review     +---------------+
+| Client |<------------------|   Approval    |
++--------+                   |   Request     |
+    |                        +---------------+
+    |
+    +-------------------+
+    |                   |
+    v                   v
++--------+         +--------+
+|Approve |         |Request |
++--------+         |Changes |
+    |              +--------+
+    |                   |
+    v                   v
++----------+       +----------+
+|  Sprint  |       | Iterate  |
+| Planning |       | Proposal |
++----------+       +----------+
+                        |
+                        +---> (Back to Step 6)
+```
+
+**Flow Description:**
+
+1. **Trigger**: Requirements approval triggers architecture spike
+2. **Context Summary**: PO summarizes client goals and constraints
+3. **Requirements Handoff**: BA receives context for deep analysis
+4. **Domain Analysis**: BA creates domain model and identifies technical needs
+5. **Architect Involvement**: Architect agent invited to spike
+6. **Collaborative Brainstorm**: PO, BA, and Architect discuss approaches
+7. **Proposal Generation**: Architecture proposal document created
+8. **ADR Creation**: Key decisions documented as ADRs
+9. **Client Presentation**: Proposal presented with rationale
+10. **Client Decision**: Approve or request changes (iterate if needed)
+
 ---
 
 ## 7. Data Requirements