feat: P2.3 Folder Sharing + P2.5 Email Import + P2.6 Contact Import + P2.7 Free/Busy

- P2.3: Folder sharing system — ShareFolderDialog, sharing-store, sharing-settings
- P2.5: Email import (.eml, .tgz, .zip) with dedup and progress
- P2.6: Contact import (vCard + CSV) with auto-mapping
- P2.7: Free/Busy view grid with color-coded slots

lib/eml-import.ts

@@ -13,6 +13,14 @@ function isZipName(name: string): boolean {
   return /\.zip$/i.test(name);
 }
 
+function isTgzName(name: string): boolean {
+  return /\.(tgz|tar\.gz)$/i.test(name);
+}
+
+function isArchiveName(name: string): boolean {
+  return isZipName(name) || isTgzName(name);
+}
+
 async function extractEmlsFromZip(file: File): Promise<ImportableEmail[]> {
   const { default: JSZip } = await import("jszip");
   const zip = await JSZip.loadAsync(await file.arrayBuffer());
@@ -30,6 +38,88 @@ async function extractEmlsFromZip(file: File): Promise<ImportableEmail[]> {
   return out;
 }
 
+async function gunzip(buffer: ArrayBuffer): Promise<ArrayBuffer> {
+  try {
+    const ds = new DecompressionStream("gzip");
+    const writer = ds.writable.getWriter();
+    const reader = ds.readable.getReader();
+
+    writer.write(new Uint8Array(buffer));
+    writer.close();
+
+    const chunks: Uint8Array[] = [];
+    while (true) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      chunks.push(value);
+    }
+
+    const totalLength = chunks.reduce((sum, c) => sum + c.length, 0);
+    const result = new Uint8Array(totalLength);
+    let offset = 0;
+    for (const chunk of chunks) {
+      result.set(chunk, offset);
+      offset += chunk.length;
+    }
+    return result.buffer;
+  } catch {
+    throw new Error("Failed to decompress gzip archive");
+  }
+}
+
+interface TarEntry {
+  name: string;
+  type: string;
+  data: ArrayBuffer;
+}
+
+function parseTar(buffer: ArrayBuffer): TarEntry[] {
+  const entries: TarEntry[] = [];
+  const view = new Uint8Array(buffer);
+  let offset = 0;
+
+  while (offset + 512 <= view.byteLength) {
+    const header = new Uint8Array(buffer, offset, 512);
+    const name = new TextDecoder().decode(header.subarray(0, 100)).replace(/\0.*$/, "");
+    const type = String.fromCharCode(header[156] || 0) || "0";
+
+    if (!name) break;
+
+    let sizeStr = "";
+    for (let i = 124; i < 136; i++) {
+      const ch = String.fromCharCode(header[i]);
+      if (ch === "\0" || ch === " ") break;
+      sizeStr += ch;
+    }
+    const size = parseInt(sizeStr || "0", 8);
+
+    offset += 512;
+
+    if (size > 0 && type === "0" && isEmlName(name)) {
+      const data = buffer.slice(offset, offset + size);
+      entries.push({
+        name: name.split(/[\\/]/).pop() || name,
+        type: "file",
+        data,
+      });
+    }
+
+    offset += Math.ceil(size / 512) * 512;
+  }
+
+  return entries;
+}
+
+async function extractEmlsFromTgz(file: File): Promise<ImportableEmail[]> {
+  const buffer = await file.arrayBuffer();
+  const decompressed = await gunzip(buffer);
+  const entries = parseTar(decompressed);
+  return entries.map((entry) => ({
+    name: entry.name,
+    blob: new Blob([entry.data], { type: EMAIL_MIME }),
+  }));
+}
+
 export async function expandImportableEmails(
   files: File[],
 ): Promise<ImportableEmail[]> {
@@ -39,10 +129,14 @@ export async function expandImportableEmails(
       out.push(...(await extractEmlsFromZip(file)));
       continue;
     }
+    if (isTgzName(file.name) || file.type === "application/gzip" || file.type === "application/x-gtar") {
+      out.push(...(await extractEmlsFromTgz(file)));
+      continue;
+    }
     const blob = new Blob([await file.arrayBuffer()], { type: EMAIL_MIME });
     out.push({ name: file.name, blob });
   }
   return out;
 }
 
-export const EML_IMPORT_ACCEPT = ".eml,.zip,message/rfc822,application/zip";
+export const EML_IMPORT_ACCEPT = ".eml,.zip,.tgz,.tar.gz,message/rfc822,application/zip,application/gzip";