[child] thesis diff/query APIs and portfolio rollup views

[adolago]

Parent epic: #481
Suggested owner role: Data API Owner

Objective:
Expose thesis diff/query APIs and portfolio-level rollup views for operators.

Dependencies:

• Depends on [child] evidence-linked thesis updates and confidence rules #510
• Depends on epic/portfolio-research-ops: portfolio-linked daily and earnings workflows #482 portfolio ops integration.

Acceptance criteria:

• Implementation plan is approved by epic owner.
• Delivery is merged with operator-facing documentation.
• Metrics/telemetry for this slice are emitted.