feat(market-implications): add transmission chain to implication cards (#2439)

Models the causal path from geopolitical event to price impact as a
2-4 node chain on each card. Each node has a label, impact_type, and
logic sentence. Nodes are tap/click-expandable inline.

- Proto: add TransmissionNode message + field 10 on MarketImplicationCard
- Seeder: prompt addition + VALID_IMPACT_TYPES validation (>=2 node gate)
- Handler: map transmission_chain snake_case -> transmissionChain camelCase
- Client: add normalizeCard() to handle both bootstrap (snake_case) and
  API (camelCase) paths; applied at both data entry points
- Renderer: renderChain() with arrow-separated nodes; delegated click
  handler collapses same node, replaces on different node click
- Tests: 4 cases covering snake/camel conversion, absent field default,
  handler backward-compat

docs/api/IntelligenceService.openapi.yaml

@@ -1834,6 +1834,19 @@ components:
                     type: string
                 driver:
                     type: string
+                transmissionChain:
+                    type: array
+                    items:
+                        $ref: '#/components/schemas/TransmissionNode'
+        TransmissionNode:
+            type: object
+            properties:
+                node:
+                    type: string
+                impactType:
+                    type: string
+                logic:
+                    type: string
         GetSocialVelocityRequest:
             type: object
         GetSocialVelocityResponse: