gui: Save PDF on every report; short and narrow windows hold up

Reports get a Save PDF button beside Copy for a spreadsheet. It typesets
the report as it's set up on screen (range, months/quarters/years,
comparison) through ledger-import's Typst statement template, the same
one the CPA package uses, in the background, writes it to the Downloads
folder (never the books: the viewer stays read-only), and opens it.

- ledger-import: Statement.percent_from marks percentage columns
  (comparison %, % of income), typeset as 12.5% with no dollar sign;
  wide statements turn the page, and past seven columns set smaller so
  a year of months fits; statement() is public for other callers.
- Compared columns that read the same (Jan 1 - Oct 12 vs a year
  earlier) now say which year, on screen and on paper.
- Short windows: the sidebar's and rail's links scroll above the status
  box instead of under it. The search palette fits the window.
- A test typesets every table-backed report from the demo books,
  plain, by month, and compared (PDF_DIR keeps the files).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-gui/src/export.rs

@@ -0,0 +1,71 @@
+//! Files the viewer makes for you (report PDFs). They go to the
+//! Downloads folder, never into the books: the viewer stays read-only.
+
+use std::path::{Path, PathBuf};
+
+/// Where saved files go: `$XDG_DOWNLOAD_DIR`, else `~/Downloads`, else
+/// the home directory.
+pub fn downloads_dir() -> PathBuf {
+    if let Some(d) = std::env::var_os("XDG_DOWNLOAD_DIR").map(PathBuf::from)
+        && d.is_dir()
+    {
+        return d;
+    }
+    let home = std::env::var_os("HOME")
+        .or_else(|| std::env::var_os("USERPROFILE"))
+        .map(PathBuf::from)
+        .unwrap_or_else(|| PathBuf::from("."));
+    let d = home.join("Downloads");
+    if d.is_dir() { d } else { home }
+}
+
+/// `name` made safe as a file name on every platform.
+pub fn file_name(name: &str, ext: &str) -> String {
+    let clean: String = name
+        .chars()
+        .map(|c| match c {
+            '/' | '\\' | ':' | '*' | '?' | '"' | '<' | '>' | '|' => '-',
+            c if c.is_control() => ' ',
+            c => c,
+        })
+        .collect();
+    format!("{}.{ext}", clean.trim())
+}
+
+/// Write `bytes` to the downloads folder as `name.ext` (replacing a file
+/// of that name: the same report renders the same bytes) and open it with
+/// the system's viewer.
+pub fn save_and_open(name: &str, ext: &str, bytes: &[u8]) -> Result<PathBuf, String> {
+    let path = downloads_dir().join(file_name(name, ext));
+    std::fs::write(&path, bytes).map_err(|e| format!("{}: {e}", path.display()))?;
+    open(&path);
+    Ok(path)
+}
+
+/// Open a file with whatever the desktop uses for its type. Best effort:
+/// the file is saved either way.
+fn open(path: &Path) {
+    #[cfg(target_os = "macos")]
+    let cmd = std::process::Command::new("open").arg(path).spawn();
+    #[cfg(target_os = "windows")]
+    let cmd = std::process::Command::new("cmd")
+        .args(["/C", "start", ""])
+        .arg(path)
+        .spawn();
+    #[cfg(not(any(target_os = "macos", target_os = "windows")))]
+    let cmd = std::process::Command::new("xdg-open").arg(path).spawn();
+    let _ = cmd;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn file_names_are_safe() {
+        assert_eq!(
+            file_name("Acme LLC — Profit and loss — Jan 1/2026: draft", "pdf"),
+            "Acme LLC — Profit and loss — Jan 1-2026- draft.pdf"
+        );
+    }
+}