Add cover page support with Chinese font rendering

Features:
- Cover page generation using Python/Pillow with Apple PingFang font
- CLI commands: cover-create, job-cover for cover page management
- API endpoints: PUT /api/fax/jobs/{id}/cover for cover modification
- Send fax with cover page: --to, --from, --subject, --note options
- Multi-page TIFF parsing for PDF conversion (fix: all pages now sent)
- Preview HTML generation with pan/zoom support
- OCR verification for cover page content
- Class 2 receive support for incoming faxes

Fixes:
- Modem initialization before Class 2 mode entry
- Dial timeout handling with retry logic
- Multi-page fax transmission between pages
- Chinese character rendering in cover pages (Apple native fonts)

Cargo.lock

@@ -262,6 +262,12 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "base64"
+version = "0.22.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
 [[package]]
 name = "bit_field"
 version = "0.10.3"
@@ -1981,6 +1987,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "axum",
+ "base64",
  "chrono",
  "clap",
  "fax",