refactor: convert to bun-workspaces monorepo (desktop/ + www/)

- Move the Tauri app (React frontend + Rust backend) into desktop/ via
  git mv — configs unchanged (relative paths: tauri.conf.json, vite.config.ts)
- Root package.json becomes a private bun workspace container with
  orchestration scripts; desktop package renamed gridline-desktop
- Scaffold www/ with Astro 7 + Tailwind v4 (hand-wired vite plugin,
  static output, ready for Dokploy)
- Update release.yml for the new layout: projectPath: desktop,
  desktop/src-tauri resource paths, rust-cache workspace path
- Update README + AGENTS.md structure trees and dev commands
- Verified: vitest (1074), cargo test (354), desktop build, tauri dev
  (window launches), tauri build (dmg + app bundles), Astro build

desktop/src/lib/csvParser.ts

@@ -0,0 +1,43 @@
+export interface ParsedCsv {
+  headers: string[];
+  rows: string[][];
+}
+
+export function parseCsv(input: string): ParsedCsv {
+  const text = input.replace(/^\uFEFF/, "");
+  if (text.trim() === "") throw new Error("CSV input is empty");
+
+  const rows: string[][] = [];
+  let field = "";
+  let row: string[] = [];
+  let inQuotes = false;
+
+  for (let i = 0; i < text.length; i++) {
+    const ch = text[i];
+    if (inQuotes) {
+      if (ch === '"') {
+        if (text[i + 1] === '"') { field += '"'; i++; }
+        else inQuotes = false;
+      } else field += ch;
+    } else if (ch === '"') {
+      inQuotes = true;
+    } else if (ch === ',') {
+      row.push(field); field = "";
+    } else if (ch === '\n' || ch === '\r') {
+      if (ch === '\r' && text[i + 1] === '\n') i++;
+      row.push(field); field = "";
+      rows.push(row); row = [];
+    } else field += ch;
+  }
+  if (field !== "" || row.length > 0) { row.push(field); rows.push(row); }
+  if (rows.length === 0) throw new Error("CSV input is empty");
+
+  const [headers, ...data] = rows;
+  const width = headers.length;
+  const padded = data.map((r) => {
+    const out = r.slice(0, width);
+    while (out.length < width) out.push("");
+    return out;
+  });
+  return { headers, rows: padded };
+}