fix(mcp): add missing meta field and consolidate documentation URLs

[bug-ops]

Summary

• Add missing meta: None field in CreateElicitationResult initializers (rmcp v1.4 breaking change)
• Consolidate documentation URLs to workspace-level book reference (https://bug-ops.github.io/zeph/)
• Remove per-crate documentation URLs—they now inherit from workspace automatically

Changes

• crates/zeph-mcp/src/client.rs: Add meta: None
• crates/zeph-mcp/src/elicitation.rs: Add meta: None
• crates/zeph-core/src/agent/mcp.rs: Add meta: None (3 initializers)
• Cargo.toml: Update workspace documentation to book URL
• crates/*/Cargo.toml: Remove per-crate documentation entries

Test plan

• `cargo check --all-targets` passes
• No new clippy warnings introduced