Add tarot readings, encrypted quote wall, display name resolution, and uptime reporting

New features:
- !tarot and !tarotspread commands with LLM-powered readings (zodiac-aware)
- !quote system with AES-256-GCM encryption at rest, reply-to-save, search, and quoteboard
- Shared crypto utility (internal/crypto) for AES-256-GCM encrypt/decrypt/HMAC
- ResolveUser now matches display names via room membership as fallback
- !vibe and !tldr show bot uptime when insufficient messages buffered

Bug fixes:
- Fix duplicate quotes table schema that would crash quotewall at runtime
- Fix biased random selection in quote retrieval (use rand.Intn)
- Fix XP rank calculation to handle tied scores with COUNT(DISTINCT xp)
- Scope all leaderboards to room members (repboard, pottyboard, insultboard, firstboard, rankings, emojiboard)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/crypto/crypto.go

@@ -0,0 +1,81 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/hex"
+	"fmt"
+)
+
+// Encrypt encrypts plaintext using AES-256-GCM with the given 32-byte key.
+// The returned ciphertext has a 12-byte random nonce prepended.
+func Encrypt(key, plaintext []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("aes new cipher: %w", err)
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("gcm new: %w", err)
+	}
+
+	nonce := make([]byte, gcm.NonceSize()) // 12 bytes
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, fmt.Errorf("generate nonce: %w", err)
+	}
+
+	ciphertext := gcm.Seal(nonce, nonce, plaintext, nil)
+	return ciphertext, nil
+}
+
+// Decrypt decrypts ciphertext produced by Encrypt. It expects the first
+// 12 bytes to be the nonce followed by the GCM-sealed data.
+func Decrypt(key, ciphertext []byte) ([]byte, error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("aes new cipher: %w", err)
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("gcm new: %w", err)
+	}
+
+	nonceSize := gcm.NonceSize()
+	if len(ciphertext) < nonceSize {
+		return nil, fmt.Errorf("ciphertext too short")
+	}
+
+	nonce, sealed := ciphertext[:nonceSize], ciphertext[nonceSize:]
+	plaintext, err := gcm.Open(nil, nonce, sealed, nil)
+	if err != nil {
+		return nil, fmt.Errorf("gcm open: %w", err)
+	}
+
+	return plaintext, nil
+}
+
+// HMAC computes HMAC-SHA256 of data with the given key and returns a hex-encoded string.
+func HMAC(key, data []byte) string {
+	mac := hmac.New(sha256.New, key)
+	mac.Write(data)
+	return hex.EncodeToString(mac.Sum(nil))
+}
+
+// ParseKey base64-decodes b64Key and validates the result is exactly 32 bytes
+// (required for AES-256).
+func ParseKey(b64Key string) ([]byte, error) {
+	key, err := base64.StdEncoding.DecodeString(b64Key)
+	if err != nil {
+		return nil, fmt.Errorf("base64 decode: %w", err)
+	}
+	if len(key) != 32 {
+		return nil, fmt.Errorf("key must be exactly 32 bytes, got %d", len(key))
+	}
+	return key, nil
+}