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.

link_composer/constants.py

@@ -0,0 +1,59 @@
+PAYLOAD_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-._~!$&'()*+,;=:@"
+QR_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:"
+
+SEGMENT_ALPHABETS = {
+  0: "0123456789",
+  1: "abcdefghijklmnopqrstuvwxyz",
+  2: "ABCDEFGHIJKLMNOPQRSTUVWXYZ",
+  3: "abcdefghijklmnopqrstuvwxyz0123456789-",
+  4: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_",
+  5: "0123456789ABCDEFabcdef",
+  6: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~!$&'()*+,;=:@",
+  7: None,  # raw UTF-8 bytes fallback
+}
+
+ALPHABET_NAMES = {
+  0: "decimal",
+  1: "lowercase",
+  2: "uppercase",
+  3: "domain-like",
+  4: "base64url-like",
+  5: "hex",
+  6: "url-safe",
+  7: "utf8-raw",
+}
+
+CODE_VERSION = 2
+SUPPORTED_CODE_VERSIONS = {1, 2}
+TLD_CODE_WIDTH = 6
+DOMAIN_CODE_WIDTH = 6
+LEGACY_DICTIONARY_CODE_WIDTH = 4
+
+CODE_PREFIX_PAYLOAD = "u"
+CODE_PREFIX_QR = "Q"
+MODE_STRUCTURED = "structured"
+MODE_QR_STRUCTURED = "qr-structured"
+MODE_DECODED = "decoded"
+
+SCHEME_CODES = {"http": 0, "https": 1}
+CODE_SCHEMES = {value: key for key, value in SCHEME_CODES.items()}
+ALLOWED_REDIRECT_SCHEMES = {"http", "https"}
+
+COMMON_TLDS = [
+  "", "com", "org", "net", "io", "dev", "at", "de", "edu", "gov", "co", "uk",
+  "app", "ai", "me", "info", "biz", "xyz", "online", "site", "shop", "store",
+  "blog", "tech", "cloud", "digital", "tools", "software", "systems", "network",
+  "eu", "us", "ca", "au", "ch", "fr", "it", "es", "nl", "se", "no", "fi",
+  "dk", "pl", "cz", "jp", "cn", "in", "br", "ru", "tv", "fm", "to", "gg",
+]
+COMMON_DOMAINS = [
+  "", "google", "youtube", "github", "reddit", "wikipedia", "twitter", "x",
+  "facebook", "instagram", "amazon", "microsoft", "apple", "cloudflare", "stackoverflow",
+  "linkedin", "tiktok", "whatsapp", "telegram", "discord", "slack", "notion", "medium",
+  "wordpress", "openai", "anthropic", "claude", "chatgpt", "docker", "kubernetes", "terraform",
+  "githubusercontent", "gitlab", "bitbucket", "npmjs", "pypi", "python", "nodejs", "mozilla",
+  "cloudfront", "aws", "azure", "googleapis", "gstatic", "vercel", "netlify", "heroku",
+  "paypal", "stripe", "shopify", "ebay", "etsy", "twitch", "spotify", "netflix",
+  "adobe", "figma", "canva", "atlassian", "jira", "confluence", "zoom", "dropbox",
+]
+SEPARATORS = "/?&=#.:-_~%+"