feat(attedit): attribute editor dialog for blocks

Double-clicking a block reference that has attributes, or running ATTEDIT
on one, now opens an editor dialog listing every attribute (tag + editable
value) with OK / Cancel. OK writes the values back to the block, with undo
and a repaint; Cancel discards. A block with no attributes still enters
in-place block edit (REFEDIT) on double-click as before. (#192)

ATTEDIT opens the dialog directly when a suitable block is already
selected; otherwise it runs the pick command and the dialog opens once a
block is chosen. This replaces the earlier command-line, per-attribute
prompt flow, which is removed along with its __ATTEDIT__ sentinel path and
the now-unused attedit_set_attrs trait hook; the ATTEDIT command is reduced
to a plain block picker.

The dialog is a tab-scoped in-canvas modal (Plan B): its working copy holds
a document-local handle, so closing that tab or switching away dismisses the
editor rather than risk applying edits to another tab's document.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/window/attribute_editor.rs

@@ -0,0 +1,131 @@
+//! Attribute editor dialog — edit the attribute values of a single block
+//! reference (INSERT). Opened by double-clicking a block that carries
+//! attributes, or by the ATTEDIT command with such a block selected.
+//!
+//! Each attribute is one row: its tag (read-only) and an editable value box.
+//! OK writes every value back to the block; Cancel (the ✕ or button) discards.
+//! The heavy lifting — applying edits, undo, repaint — lives in the update
+//! handler (`Message::AttrEditorOk`); this module is pure layout.
+
+use crate::app::Message;
+use iced::widget::{button, column, container, row, scrollable, text, text_input, Space};
+use iced::{Background, Border, Color, Element, Length, Theme};
+
+const BG: Color = Color { r: 0.15, g: 0.15, b: 0.15, a: 1.0 };
+const WHITE: Color = Color { r: 0.92, g: 0.92, b: 0.92, a: 1.0 };
+const DIM: Color = Color { r: 0.55, g: 0.55, b: 0.55, a: 1.0 };
+const ACCENT: Color = Color { r: 0.30, g: 0.62, b: 0.95, a: 1.0 };
+const FIELD_BG: Color = Color { r: 0.10, g: 0.10, b: 0.10, a: 1.0 };
+const BORDER: Color = Color { r: 0.32, g: 0.32, b: 0.32, a: 1.0 };
+
+fn field_style(_t: &Theme, _s: text_input::Status) -> text_input::Style {
+    text_input::Style {
+        background: Background::Color(FIELD_BG),
+        border: Border { color: BORDER, width: 1.0, radius: 3.0.into() },
+        icon: WHITE,
+        placeholder: DIM,
+        value: WHITE,
+        selection: ACCENT,
+    }
+}
+
+/// Build the attribute editor dialog body. `block` is the reference's block
+/// name (shown as a subtitle); `fields` are the `(tag, value)` pairs in
+/// attribute order — the row index is the routing key back to
+/// `Message::AttrEditorInput`.
+pub fn view_window<'a>(block: &'a str, fields: &'a [(String, String)]) -> Element<'a, Message> {
+    let mut list = column![].spacing(6);
+    for (idx, (tag, value)) in fields.iter().enumerate() {
+        let value_box = text_input("", value)
+            .on_input(move |v| Message::AttrEditorInput { idx, value: v })
+            .on_submit(Message::AttrEditorOk)
+            .style(field_style)
+            .size(13)
+            .padding([4, 6])
+            .width(Length::Fill);
+
+        let attr_row = row![
+            container(text(tag.as_str()).size(13).color(WHITE))
+                .width(170)
+                .padding([4, 6]),
+            value_box,
+        ]
+        .spacing(8)
+        .align_y(iced::Center);
+        list = list.push(attr_row);
+    }
+
+    let body: Element<'_, Message> = if fields.is_empty() {
+        text("This block has no attributes.")
+            .size(13)
+            .color(DIM)
+            .into()
+    } else {
+        scrollable(list).height(Length::Fill).into()
+    };
+
+    let ok = button(text("OK").size(13).color(WHITE))
+        .padding([5, 22])
+        .on_press(Message::AttrEditorOk)
+        .style(|_: &Theme, status| {
+            let bg = if matches!(status, button::Status::Hovered | button::Status::Pressed) {
+                Color { r: 0.32, g: 0.55, b: 0.85, a: 1.0 }
+            } else {
+                ACCENT
+            };
+            button::Style {
+                background: Some(Background::Color(bg)),
+                text_color: WHITE,
+                border: Border { radius: 4.0.into(), ..Default::default() },
+                ..Default::default()
+            }
+        });
+
+    let cancel = button(text("Cancel").size(13).color(WHITE))
+        .padding([5, 18])
+        .on_press(Message::CloseModal)
+        .style(|_: &Theme, status| {
+            let bg = if matches!(status, button::Status::Hovered | button::Status::Pressed) {
+                Color { r: 0.28, g: 0.28, b: 0.28, a: 1.0 }
+            } else {
+                Color { r: 0.20, g: 0.20, b: 0.20, a: 1.0 }
+            };
+            button::Style {
+                background: Some(Background::Color(bg)),
+                text_color: WHITE,
+                border: Border { color: BORDER, width: 1.0, radius: 4.0.into() },
+                ..Default::default()
+            }
+        });
+
+    let header = column![
+        text("Edit Attributes").size(18).color(WHITE),
+        text(format!("Block: {block}")).size(12).color(DIM),
+    ]
+    .spacing(2);
+
+    container(
+        column![
+            header,
+            Space::new().height(10),
+            body,
+            Space::new().height(12),
+            row![
+                Space::new().width(Length::Fill),
+                cancel,
+                Space::new().width(8),
+                ok
+            ]
+            .align_y(iced::Center),
+        ]
+        .padding(4),
+    )
+    .style(|_: &Theme| container::Style {
+        background: Some(Background::Color(BG)),
+        ..Default::default()
+    })
+    .width(Length::Fill)
+    .height(Length::Fill)
+    .padding(14)
+    .into()
+}