docs: broaden audience (managed providers of any size, multi-runtime hint) + unify blueprint mermaid theming

[pallakatos]

Follow-up polish on top of #47 / #48.

README

• Add an explicit hint near the top that today AzureClaw hosts OpenClaw, but the same guardrails extend to any agentic runtime in future. The plugin/tools.deny hook is the OpenClaw-specific bit; the rest (WI-fronted inference, Confidential Containers, Signal-Protocol mesh, AGT, audit chain) is runtime-agnostic. MCP / A2A / AP2 scaffolding already in the codebase → same sandbox can host LangGraph, AutoGen, CrewAI, Semantic Kernel etc. over the wire.
• Add a Hardware-isolated cloud offload bullet that points at Blueprint 03, framed as 'not just for enterprises' — any managed provider (small MSPs, indie SaaS, hobbyist co-ops) can use the same primitives to offer a confidential sandbox to end users whose home setup doesn't fit the job (heavier models, longer runs, parallel fan-out, premium-quota work).

Blueprint 03

• Reframe the persona from "SaaS provider" to "managed-AzureClaw provider at any scale".
• Add concrete customer examples (indie devs, researchers parallelising prompts overnight, field engineers, privacy-sensitive users, enterprises picking smaller specialists).
• Spell out that the security shape is identical regardless of provider size — only the economic shape changes.

Mermaid theming

• Add a unified %%{init}%% theme directive (theme: base with neutral slate themeVariables) to all 15 mermaid blocks across blueprints 01–05 so they render consistently in both GitHub light and dark mode (previously some blocks looked dark, others light, depending on which classDef colours dominated).
• Normalise one outlier in 02 (boundary fill #f0f7ff → #dbeafe) so the cool-blue boundary shade matches the cool-blue "provider" shade already used in 03 and 04.

Docs-only. No runtime / API surface changes.