refactor: complete Phase 13 deep architecture refactoring (etaps 3-7)

Split monolithic files into modular architecture:
- ui/messages.rs (893→365 lines): extract modals/, compose_bar.rs
- tdlib/messages.rs (836→3 files): split into messages/mod, convert, operations
- config/mod.rs (642→3 files): extract validation.rs, loader.rs
- Code duplication cleanup: shared components, ~220 lines removed
- Documentation: PROJECT_STRUCTURE.md rewrite, 16 files got //! docs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ui/modals/pinned.rs

@@ -0,0 +1,93 @@
+//! Pinned messages viewer modal
+
+use crate::app::App;
+use crate::tdlib::TdClientTrait;
+use crate::ui::components::{render_message_item, calculate_scroll_offset, render_help_bar};
+use ratatui::{
+    layout::{Constraint, Direction, Layout, Rect},
+    style::{Color, Modifier, Style},
+    text::{Line, Span},
+    widgets::{Block, Borders, Paragraph},
+    Frame,
+};
+
+/// Renders pinned messages mode
+pub fn render<T: TdClientTrait>(f: &mut Frame, area: Rect, app: &App<T>) {
+    // Извлекаем данные из ChatState
+    let (messages, selected_index) = if let crate::app::ChatState::PinnedMessages {
+        messages,
+        selected_index,
+    } = &app.chat_state
+    {
+        (messages.as_slice(), *selected_index)
+    } else {
+        return; // Некорректное состояние
+    };
+
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([
+            Constraint::Length(3), // Header
+            Constraint::Min(0),    // Pinned messages list
+            Constraint::Length(3), // Help bar
+        ])
+        .split(area);
+
+    // Header
+    let total = messages.len();
+    let current = selected_index + 1;
+    let header_text = format!("📌 ЗАКРЕПЛЁННЫЕ ({}/{})", current, total);
+    let header = Paragraph::new(header_text)
+        .block(
+            Block::default()
+                .borders(Borders::ALL)
+                .border_style(Style::default().fg(Color::Magenta)),
+        )
+        .style(
+            Style::default()
+                .fg(Color::Magenta)
+                .add_modifier(Modifier::BOLD),
+        );
+    f.render_widget(header, chunks[0]);
+
+    // Pinned messages list
+    let content_width = chunks[1].width.saturating_sub(2) as usize;
+    let mut lines: Vec<Line> = Vec::new();
+
+    for (idx, msg) in messages.iter().enumerate() {
+        if idx > 0 {
+            lines.push(Line::from(""));
+        }
+        lines.extend(render_message_item(msg, idx == selected_index, content_width, 3));
+    }
+
+    if lines.is_empty() {
+        lines.push(Line::from(Span::styled(
+            "Нет закреплённых сообщений",
+            Style::default().fg(Color::Gray),
+        )));
+    }
+
+    // Скролл к выбранному сообщению
+    let scroll_offset = calculate_scroll_offset(selected_index, 5, chunks[1].height);
+
+    let messages_widget = Paragraph::new(lines)
+        .block(
+            Block::default()
+                .borders(Borders::ALL)
+                .border_style(Style::default().fg(Color::Magenta)),
+        )
+        .scroll((scroll_offset, 0));
+    f.render_widget(messages_widget, chunks[1]);
+
+    // Help bar
+    let help = render_help_bar(
+        &[
+            ("↑↓", "навигация", Color::Yellow),
+            ("Enter", "перейти", Color::Green),
+            ("Esc", "выход", Color::Red),
+        ],
+        Color::Magenta,
+    );
+    f.render_widget(help, chunks[2]);
+}