Initial implementation of Improvise TUI

Multi-dimensional data modeling terminal application with:
- Core data model: categories, items, groups, sparse cell store
- Formula system: recursive-descent parser, named formulas, WHERE clauses
- View system: Row/Column/Page axes, tile-based pivot, page slicing
- JSON import wizard (interactive TUI + headless auto-mode)
- Command layer: all mutations via typed Command enum for headless replay
- TUI: Ratatui grid, tile bar, formula/category/view panels, help overlay
- Persistence: .improv (JSON), .improv.gz (gzip), CSV export, autosave
- Static binary via x86_64-unknown-linux-musl + nix flake devShell
- Headless mode: --cmd '{"op":"..."}' and --script file.jsonl

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

src/ui/tile_bar.rs

@@ -0,0 +1,82 @@
+use ratatui::{
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Modifier, Style},
+    widgets::Widget,
+};
+
+use crate::model::Model;
+use crate::view::Axis;
+use crate::ui::app::AppMode;
+
+pub struct TileBar<'a> {
+    pub model: &'a Model,
+    pub mode: &'a AppMode,
+}
+
+impl<'a> TileBar<'a> {
+    pub fn new(model: &'a Model, mode: &'a AppMode) -> Self {
+        Self { model, mode }
+    }
+}
+
+impl<'a> Widget for TileBar<'a> {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let view = match self.model.active_view() {
+            Some(v) => v,
+            None => return,
+        };
+
+        let selected_cat_idx = if let AppMode::TileSelect { cat_idx } = self.mode {
+            Some(*cat_idx)
+        } else {
+            None
+        };
+
+        let mut x = area.x + 1;
+        buf.set_string(area.x, area.y, " Tiles: ", Style::default().fg(Color::Gray));
+        x += 8;
+
+        let cat_names: Vec<&str> = self.model.category_names();
+        for (i, cat_name) in cat_names.iter().enumerate() {
+            let axis = view.axis_of(cat_name);
+            let axis_symbol = match axis {
+                Axis::Row => "↕",
+                Axis::Column => "↔",
+                Axis::Page => "☰",
+                Axis::Unassigned => "─",
+            };
+
+            let label = format!(" [{cat_name} {axis_symbol}] ");
+            let is_selected = selected_cat_idx == Some(i);
+
+            let style = if is_selected {
+                Style::default().fg(Color::Black).bg(Color::Cyan).add_modifier(Modifier::BOLD)
+            } else {
+                match axis {
+                    Axis::Row => Style::default().fg(Color::Green),
+                    Axis::Column => Style::default().fg(Color::Blue),
+                    Axis::Page => Style::default().fg(Color::Magenta),
+                    Axis::Unassigned => Style::default().fg(Color::DarkGray),
+                }
+            };
+
+            if x + label.len() as u16 > area.x + area.width { break; }
+            buf.set_string(x, area.y, &label, style);
+            x += label.len() as u16;
+        }
+
+        // Hint
+        if matches!(self.mode, AppMode::TileSelect { .. }) {
+            let hint = " [Enter] cycle axis  [r/c/p] set axis  [←→] select  [Esc] cancel";
+            if x + hint.len() as u16 <= area.x + area.width {
+                buf.set_string(x, area.y, hint, Style::default().fg(Color::DarkGray));
+            }
+        } else {
+            let hint = " Ctrl+↑↓←→ to move tiles";
+            if x + hint.len() as u16 <= area.x + area.width {
+                buf.set_string(x, area.y, hint, Style::default().fg(Color::DarkGray));
+            }
+        }
+    }
+}