Expose dossier API and frontend viewer/export for AP engine

[clementinestetai]

Problem

Even if we build the dossier pipeline, it will not be useful unless users can request it, inspect it, and export it in a stable format.

The current market-intel UI and research exports are not designed for a per-target opposing-side memo workflow.

What to build

• API endpoints to build/fetch dossier payloads
• JSON and markdown export formats for the AP engine
• Frontend dossier viewer with source list, issue list, and executive summary
• Ability to filter by target/deal and view run history

Acceptance criteria

• A user can request the latest dossier for a target via API
• The dossier can be exported as structured JSON for the AP engine
• The frontend can display the dossier summary and supporting sources
• The export format is stable and documented