chore: glow up README + diagrams — hero banner, marketing callout

[brentrager]

Applies the Smoo AI README glow-up (v2) to smooth (the th CLI), using the shared Smoo-family banner generator for a consistent sub-brand look.

What changed

• Hero banner — replaced the logo + H1 + tagline block with a gradient .github/banner.png (shared Smoo family mark, "smooth" name, tagline, kicker). SVG source kept alongside.
• Badges — the 3 primary badges (The Line, Smoo AI platform, license) are now for-the-badge + labelColor=020618; Rust/release badges stay flat-square.
• Marketing callout — Part of Smoo AI now leads with smoo.ai/th and links sibling repos (smooth-operator, deploy, logger, config).
• Diagrams (5) — all five mermaid blocks rebranded with the dark init directive + warm/teal classDefs (dropping the off-brand per-node style lines and the elk renderer override) and simplified:
  • Agent loop — collapsed verbose <small> labels, chained edges.
  • Architecture — collapsed the 3-operative fan-out and the host sub-services into single nodes; one flowchart TB.
  • Inside each MicroVM — merged Narc's two edges, shortened port labels.
  • Security model — collapsed tool/pearl/MCP allowlists into one node, trimmed labels; kept the 3-tier subgraphs.
  • Access negotiation (sequenceDiagram) — themed actors/notes to the brand palette.

All real content (install, CLI reference, cast table, tech stack, workspace layout, dev commands) preserved. No .smooth/dolt touched.

🤖 Generated with Claude Code

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