docs: reorganize into en/ru and add English translation

docs/en/modules/07-app-perf.md

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+# App and Perf modules
+
+## `src/app.rs` — GlintApp
+
+Iced application entry point. Holds state and implements `update`/`view`.
+
+### `GlintApp`
+
+```rust
+pub struct GlintApp {
+    pub doc:        Document<'static>,
+    pub vdom_roots: Vec<Element<'static>>,
+    pub rhei:       RheiContext,
+}
+```
+
+- `doc` — original Document (styles, variables, tracker)
+- `vdom_roots` — result of the last evaluate_vdom (_incr)
+- `rhei` — Rhai engine with cached ASTs
+
+### `update(&mut self, message: Message) -> iced::Task<Message>`
+
+Processing messages from Iced:
+
+| Message | Action |
+|---------|--------|
+| `WindowScrolled(y)` | Set `__scroll_y`, call `on_variable_changed` |
+| `ScrollableScrolled(id, y)` | Set `__scroll_{id}`, call `on_variable_changed` |
+| `EventTriggered(script)` | `execute_action()`, then diff variables to find changed ones |
+| `InputChanged(var, val)` | Set variable, call `on_variable_changed` |
+| `ToggleChanged(var, val)` | Set `Bool`, call `on_variable_changed` |
+| `SliderChanged(var, val)` | Set `Float`, call `on_variable_changed` |
+
+After processing the message:
+1. `tracker.take_dirty_set()` — get dirty elements
+2. `evaluate_vdom_incr()` — recalculate VDOM
+3. Save to `self.vdom_roots`
+
+**Perf:** VDOM phase is measured with `PerfScope::new("vdom")`.
+
+### `view(&self) -> iced::Element`
+
+Build Iced widgets from `self.vdom_roots`:
+
+1. Collect scroll_positions from `__scroll_*` variables
+2. For each root: `render_element()` → push into column
+3. Overlay global fixed/absolute/sticky layers
+4. Return `container(layout).into()`
+
+**Perf:** Render phase is measured with `PerfScope::new("render")`.
+At the end `perf::print_frame()` — output to stderr.
+
+---
+
+## `src/perf.rs` — Performance Monitoring
+
+Phase timing system (VDOM, Style, Render). Enabled with `--perf` flag.
+
+### `PerfReport`
+
+```rust
+pub struct PerfReport {
+    pub vdom_eval: f64,  // ms
+    pub style: f64,      // ms
+    pub render: f64,     // ms
+    pub total: f64,      // ms
+}
+```
+
+Stored in `thread_local!` `RefCell<PerfReport>`.
+
+### `PerfScope`
+
+Drop-guard: measures time from creation to destruction.
+
+```rust
+pub struct PerfScope {
+    name: &'static str,
+    start: Instant,
+}
+```
+
+On `drop()`: adds elapsed ms to the corresponding `PerfReport` field.
+Names: `"vdom"`, `"style"`, `"render"`.
+
+### Functions
+
+| Function | Description |
+|----------|-------------|
+| `set_enabled(bool)` | Enable/disable measurements |
+| `is_enabled() -> bool` | Check state |
+| `report_and_reset() -> Option<String>` | Collect report, check >16ms threshold |
+| `reset()` | Reset PerfReport |
+| `print_frame()` | Call report_and_reset + reset, print to stderr |
+
+### Example output
+
+```
+[perf] VDOM: 6.63ms | Style: 0.26ms | Render: 7.19ms | Total: 14.08ms
+[perf] VDOM: 13.26ms | Style: 0.52ms | Render: 7.18ms | Total: 20.95ms ⚠️ Frame budget exceeded! 20.95ms > 16ms
+```
+
+### Instrumentation points
+
+| File | Phase | Location |
+|------|-------|----------|
+| `app.rs:update` | vdom | Around `evaluate_vdom_incr()` |
+| `app.rs:view` | render | Entire `view()` function |
+| `style.rs:compute_cached` | style | Inside `StyleSheet::compute_cached()` |