feat: add self-contained link composer

- Add structured URL codec with compact alphabets and dictionary support.
- Add public decode, redirect, and QR endpoints for composed links.
- Add authenticated encode API and link composer UI.
- Generate PNG QR codes via qrcode with Pillow support.
- Register the new blueprint and navigation entry.
- Cover public decode, auth gating, redirect URL parsing, and QR output.
- Bump NanoShare to 1.27.0 and lock new dependencies.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "nanoshare"
-version = "1.26.0"
+version = "1.27.0"
 description = "Add your description here"
 readme = "README.md"
 requires-python = ">=3.13"
@@ -16,6 +16,7 @@ dependencies = [
     "quart==0.20.0",
     "quart-flask-patch==0.3.0",
     "quart-session",
+    "qrcode[pil]>=8.0",
     "redis==7.4.0",
 ]