feat(PORT-001A): add collateral entry basis settings

docs/ROADMAP.md

@@ -272,13 +272,30 @@ DATA-001 (Price Feed)
 
 **Dependencies:** stable deployed app on VPS
 
+### PORT-001A: Collateral Entry Basis in Settings [P1, M] **[depends: PORT-001]**
+**As a** portfolio manager, **I want** to store my collateral entry basis **so that** the dashboard can derive position size consistently from either cost basis or weight. 
+
+**Acceptance Criteria:**
+- Settings supports entering either:
+  - total collateral start value **and** entry price, or
+  - gold weight directly
+- Updating one mode calculates the other representation automatically
+- Persist both the chosen input mode and the derived values needed by the app
+- Validation prevents impossible or contradictory values (zero/negative price, value, or weight)
+- UI makes the relationship explicit: `weight = start_value / entry_price`
+- Browser-visible test covers switching modes and saving derived values
+
+**Technical Notes:**
+- Extend `PortfolioConfig` / settings persistence with entry-basis fields
+- Keep overview and other consumers compatible with existing portfolio settings
+- Prefer a single canonical stored representation plus derived display fields to avoid drift
+
+**Dependencies:** PORT-001
+
 ## Implementation Priority Queue
 
-1. **DATA-002A** - Fix options UX/performance regression
-2. **DATA-001A** - Remove misleading mock overview price
-3. **OPS-001** - Add Caddy route once app behavior is stable
-4. **DATA-003** - Risk metrics
-5. **PORT-002** - Risk management safety
-6. **EXEC-001** - Core user workflow
-7. **EXEC-002** - Execution capability
-8. Remaining features
+1. **PORT-001A** - Add collateral entry basis and derived weight/value handling in settings
+2. **PORT-002** - Risk management safety
+3. **EXEC-001** - Core user workflow
+4. **EXEC-002** - Execution capability
+5. Remaining features