docs(launch): marketing assets (logo/SVG/banner) for v1.0-rc1 launch

[trilamsr]

Context

Tier-2 C launch-artifacts polish path. PR #473 shipped 3 launch docs (announcement / demo / FAQ) + README index. README explicitly notes a marketing-asset gap: no logo, SVG, or social banner placeholder.

Scope

Pre-GA polish:

• Logo (SVG, two-color minimum, GitHub README rendering safe).
• Social banner (1500×500 for Twitter/X; 1200×630 OG).
• Optionally: favicon and 256×256 raster fallback.
• Place under docs/launch/assets/ with usage notes in docs/launch/README.md.

Refs

PR #473, #488 (wave-2 audit), Tier-2 C cut-criterion.