[Docs] Rewrite README around workflow-first MCP UX

[StatPan]

Parent: #60
Depends on: #62 and the first accepted workflow contract.

Goal

Rewrite the public README after the UX contract stabilizes so users see AssemblyMCP as a legislative research MCP, not only a National Assembly API wrapper.

Scope

• Organize README by user jobs and tool groups.
• Keep raw discovery documented as a fallback path.
• Add examples for stdio/uvx and Streamable HTTP /mcp.
• Document failure markers and how LLM clients should react.
• Keep README_EN in sync.

Acceptance Criteria

• README reflects the actual public MCP tool surface.
• README_EN is updated in the same PR.
• Examples start with workflow tools before raw API tools.
• Failure marker semantics are documented.
• No unreleased tool names are advertised unless clearly marked as planned.