Release v2.8 — conversational memory, one-click pivots, reasoning-model fix
Merges feature/v2.8:
- Session-scoped follow-up chat grounded in each investigation
- One-click suggested pivots that launch a new investigation
- Fix blank Findings for reasoning models (o1 / DeepSeek-R1) — #137
- Strict-grounding rule on summary presets
- Investigation output reformatted as Markdown headings + bullets
- Prompt-template brace-injection hardening