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/sethvargo/go-retry/backoff_constant.go

@@ -0,0 +1,25 @@
+package retry
+
+import (
+	"context"
+	"time"
+)
+
+// Constant is a wrapper around Retry that uses a constant backoff. It panics if
+// the given base is less than zero.
+func Constant(ctx context.Context, t time.Duration, f RetryFunc) error {
+	return Do(ctx, NewConstant(t), f)
+}
+
+// NewConstant creates a new constant backoff using the value t. The wait time
+// is the provided constant value. It panics if the given base is less than
+// zero.
+func NewConstant(t time.Duration) Backoff {
+	if t <= 0 {
+		panic("t must be greater than 0")
+	}
+
+	return BackoffFunc(func() (time.Duration, bool) {
+		return t, false
+	})
+}