feat: add end-to-end benchmark for contact-book-manager app

[akroshg]

Add a criterion-based end-to-end benchmark that compiles the real contact-book-manager templates into a protocol binary and measures performance across three areas:

• Protocol deserialization measures WebUIProtocol::from_protobuf() throughput
• Handler rendering (no plugin) renders the dashboard page at 10 / 100 / 1,000 contacts
• Handler rendering (FastHydration plugin) same with hydration markers enabled

Key design choices

• Always fresh protocol templates are compiled via webui::build() at benchmark time from examples/app/contact-book-manager/src/. No cached binary template changes are automatically reflected in the next run.
• Realistic state contacts are generated with names, emails, phones, companies, groups, favorites, and addresses matching the app's state.json schema.
• Summary table a compact performance report (Iters, Avg, Min, Max, Dev%, P50, P90, P99, IQR, Bytes) is printed after criterion finishes for easy sharing.

Quality gate integration

• cargo xtask check now includes a bench (validate) step that runs --test mode (compile + one iteration per benchmark) to catch breakage early.
• cargo xtask bench webui runs the full contact-book benchmark with measurements.

Files changed

File	Change
crates/webui/benches/contact_book_bench.rs	New benchmark file (602 lines)
crates/webui/benches/README.md	Usage docs, result interpretation, regression detection
crates/webui/Cargo.toml	Add criterion, webui-handler, webui-protocol dev-deps + [[bench]]
xtask/src/main.rs	Add bench validate step to check, add webui bench target
Cargo.lock	Lockfile update

Running

# Quick validation
cargo bench -p webui --bench contact_book_bench -- --test

# Full benchmark
cargo bench -p webui --bench contact_book_bench

# Via xtask
cargo xtask bench webui

[akroshg]

Output when run with command: cargo bench -p webui --bench contact_book_bench

============================= WebUI Contact Book — Performance Summary =============================
Story                     Iters   Avg(ms)       Min       Max   Dev%       P50       P90       P99       IQR     Bytes
----------------------------------------------------------------------------------------------------
ProtocolParse             56144      0.05      0.04      2.70  34.8%      0.04      0.04      0.07      0.00     28538
Render/10                  4783      0.63      0.61      1.29   6.3%      0.62      0.64      0.72      0.02     25960
Render/100                  620      4.84      4.70      7.14   4.0%      4.79      4.97      5.65      0.10     56397
Render/1000                  54     56.31     52.49     61.78   4.0%     56.39     59.16     61.10      3.60    362930
RenderFAST/10              4640      0.65      0.62      1.85   6.0%      0.64      0.67      0.80      0.03     31052
RenderFAST/100              606      4.96      4.84      8.69   5.3%      4.92      5.00      5.64      0.05     68149
RenderFAST/1000              52     57.83     52.92     65.56   4.9%     57.46     60.86     65.35      2.53    443082
====================================================================================================
IQR = P75 − P25 (lower means more consistent)
All times in milliseconds
====================================================================================================

[akroshg]

Fixes #69