refactor(hooks): replace lock_scroll.js with Rust web_sys implementation

[mp-c0de]

Summary

Resolves #1.

Replaces public/hooks/lock_scroll.js (254 lines of vanilla JS) with a pure Rust implementation using web_sys. The new module lives in app_crates/registry/src/hooks/scroll_lock.rs and exposes the same API:

• lock() — locks scroll on body + all scrollable containers, compensates scrollbar width
• unlock(delay_ms) — restores scroll after optional delay (for exit animations)
• is_locked() — returns current lock state

The Rust implementation:

• Batches DOM reads before writes to minimise reflows (matching the JS behaviour)
• Registers window.ScrollLock via wasm_bindgen closures so existing inline scripts work unchanged
• Uses thread_local! { RefCell } for state (wasm is single-threaded)
• Preserves the same exclusion list (ScrollArea, CommandList, SelectContent, etc.)
• Handles scrollbar width compensation on fixed-position elements

Changes

• New: app_crates/registry/src/hooks/scroll_lock.rs — full Rust implementation
• Modified: Cargo.toml — added CssStyleDeclaration to web-sys features
• Modified: app/src/app.rs — calls scroll_lock::init() at app startup (wasm-only via #[cfg])
• Modified: app/src/shell.rs — removed global <script async src="/hooks/lock_scroll.js">
• Modified: 8 component files — removed <script src="/hooks/lock_scroll.js"> from Sheet, Dialog, Select, DropdownMenu, MultiSelect, Command, Menubar, ContextMenu
• Deleted: public/hooks/lock_scroll.js

Not included (follow-up work)

• Regenerating public/registry/ files (tree.md, component markdown)
• Updating crates/ui-cli/ test fixtures that reference lock_scroll.js
• Adding the missing Playwright test cases (scrollbar compensation, unlock delay, nested containers)

Test plan

• Verified cargo check compiles with zero errors on scroll_lock.rs
• Ran cargo leptos watch — server starts without panics
• Tested Dialog component — scroll locks on open, restores on close
• Tested Sheet component — scroll locks on open, restores after animation delay
• Verified window.ScrollLock is registered and isLocked() returns correct state
• Run existing Playwright e2e tests for all 8 affected components
• Run use-lock-body-scroll.spec.ts hook test

[mp-c0de]

Also fixes #23 (Safari tab buttons)

While testing this PR I discovered it incidentally fixes #23 as well. The inline <script src="/hooks/lock_scroll.js"></script> tags this PR removes were causing a hydration crash in Safari (tachys finds the <script> where it expects a Leptos marker comment), which silently broke all reactive interactivity on docs pages.

Verified by A/B testing — clean main reproduces the Safari cold-start hydration error every time, applying this PR fixes it on first load every time.

Full root cause analysis in #23.