fix(cdp,mcp): stabilize page linting noise

[aram-devdocs]

Summary

• wait for initialized CDP documents before reuse and navigate data: documents through CDP instead of script assignment
• guard MCP lint_page_html documents with a fetch-blocking CSP while preserving doctype/head placement
• ignore hidden Next.js route-announcer spacing infrastructure and update the Next e2e baseline

Verification

• cargo fmt --all -- --check
• cargo test -p plumb-cdp --lib
• cargo test -p plumb-core --test golden_spacing_grid --test golden_spacing_scale
• cargo test -p plumb-mcp --lib lint_page_html_guarded_document
• cargo test -p plumb-mcp --all-features --test mcp_protocol lint_page_html -- --nocapture
• cargo clippy -p plumb-core -p plumb-cdp -p plumb-mcp --all-targets --all-features -- -D warnings
• RUSTDOCFLAGS=-Dwarnings cargo doc --workspace --no-deps
• cargo build --release -p plumb-cli
• PLUMB_BIN=target/release/plumb scripts/noise-scoreboard.sh --live
• just validate
• cargo run --release -p plumb-e2e -- --all --no-build --plumb-bin target/release/plumb --chrome-path "/tmp/plumb-cft150/chrome-mac-arm64/Google Chrome for Testing.app/Contents/MacOS/Google Chrome for Testing"

Dogfood: release MCP lint_page_html against Vertice Labs raw page HTML now returns isError=false instead of timing out on data:.

[github-actions]

I have enough data to compose the final review. Let me confirm one more item.