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.

run.py

@@ -11,6 +11,7 @@ from routes import (
   basic_bp, auth_login_bp,
   side_main_bp,
   upload_bp,
+  link_composer_bp,
   cli_auth_bp,
   api_download_bp,
   api_events_bp,
@@ -24,6 +25,7 @@ app.register_blueprint(auth_login_bp)
 
 app.register_blueprint(side_main_bp)
 app.register_blueprint(upload_bp)
+app.register_blueprint(link_composer_bp)
 app.register_blueprint(cli_auth_bp)
 app.register_blueprint(api_download_bp)
 app.register_blueprint(api_events_bp)