[EPIC] Ecosystem launch — landing page & cross-library story (dynavec / dynaflow / dynalogs / dynaevals) #276

Introduce the four-pillar ecosystem publicly: dynavec (Remember), dynaflow (Build & run), dynalogs (Observe), dynaevals (Measure & improve) — one library, one install, one cloud account. Covers the landing page sections, the docs ecosystem overview, README updates, and the positioning vs LangChain/LangGraph.

Tracks the child issues below; see roadmap §1 (vision) and the ecosystem table.

Child issues

• Landing page: ecosystem section introducing the four pillars #309 Landing page: ecosystem section introducing the four pillars
• Landing page: "How they fit together" diagram #310 Landing page: "How they fit together" diagram
• Landing page: positioning vs LangChain / LangGraph (parity + differentiators) #311 Landing page: positioning vs LangChain / LangGraph (parity + differentiators)
• Docs: ecosystem overview page in the docs site #312 Docs: ecosystem overview page in the docs site
• README: add ecosystem section + roadmap link #313 README: add ecosystem section + roadmap link
• Commit the roadmap doc into the repo (docs/roadmap.md) #314 Commit the roadmap doc into the repo (docs/roadmap.md)