feat(confidence-engine): v0.59b-c — report freshness on Report page + Portfolio

v0.59b — Report page freshness UI:
- Shows Current / Update available beside the generated report
- Manual Update report action with duplicate prevention guard
- Explanation copy about investigation changes since generation
- Persists generatedFromRevision during update flow

v0.59c — Portfolio Report freshness state:
- Surfaces Current / Update available alongside existing View report link
- Derives solely from revision provenance (zero model calls)
- No Update report action on Portfolio (manual update owned by Report page)
- Neither state shown when no Report exists
- Updated makeSnapshot with investigationRevision for realistic test data

tests/ui/investigation-overview-ui.test.jsx

@@ -56,6 +56,7 @@ function makeSnapshot(overrides = {}) {
     updatedAt: new Date().toISOString(),
     schemaVersion: 1,
     investigationReport: null,
+    investigationRevision: 0,
     findings: [],
     ...overrides,
   };
@@ -113,6 +114,7 @@ describe("Portfolio page (pre-confirmation v0.55/v0.56)", () => {
         investigationReport: {
           understanding: "We understand complaints rose.",
           hasPlausibleInterpretations: false,
+          generatedFromRevision: 0,
         },
       }),
     );
@@ -161,6 +163,7 @@ describe("Portfolio page (pre-confirmation v0.55/v0.56)", () => {
         investigationReport: {
           understanding: "We understand complaints rose.",
           hasPlausibleInterpretations: false,
+          generatedFromRevision: 0,
         },
       }),
     );