Initial lookbook implementation

Pinterest-style visual bookmarking app with:
- URL metadata extraction (OG/Twitter meta, oEmbed fallback)
- Image caching in Postgres with 480px thumbnails
- Multi-tag filtering with Ctrl/Cmd for OR mode
- Fuzzy tag suggestions and inline tag editing
- Browser console auth() with first-use password setup
- Brutalist UI with Commit Mono font and Pico CSS
- Light/dark mode via browser preference

vendor/github.com/cespare/xxhash/v2/xxhash_safe.go

@@ -0,0 +1,16 @@
+//go:build appengine
+// +build appengine
+
+// This file contains the safe implementations of otherwise unsafe-using code.
+
+package xxhash
+
+// Sum64String computes the 64-bit xxHash digest of s with a zero seed.
+func Sum64String(s string) uint64 {
+	return Sum64([]byte(s))
+}
+
+// WriteString adds more data to d. It always returns len(s), nil.
+func (d *Digest) WriteString(s string) (n int, err error) {
+	return d.Write([]byte(s))
+}