Replace monolithic Overview-style reporting with composable 2.x projections

[Tim55667757]

Goal

Retire presentation-heavy monolithic reporting patterns in favor of composable domain queries and renderers.

Scope

• Decompose current overview/report responsibilities into reusable queries and projections.
• Keep portfolio/account/analytics calculations independent.
• Compose high-level reports from reusable projection blocks.
• Define migration behavior for legacy Overview-style APIs without preserving unnecessary internal structure.
• Avoid recreating 1.x output coupling inside the new architecture.

Acceptance criteria

• High-level overview output is composed from reusable projections.
• Calculation, enrichment, and rendering are separate concerns.
• Legacy presentation-heavy internals are not required by the 2.x core.
• Migration guidance clearly distinguishes compatibility shims from canonical 2.x APIs.