feat(auth-jwt): initial implementation — JWT lifecycle and AuthMiddleware (v1.0.0)

Introduces code.nochebuena.dev/einherjar/auth-jwt — JWT authentication middleware
and token lifecycle management for the Einherjar framework. Absorbs httpauth-jwt
from micro-lib with three changes: logger parameter on AuthMiddleware, httputil.Error
for consistent 401 responses, and added ECDSA support.

Signers and Verifiers (one file per implementation — CT-6 compliant):
- Verifier interface — Verify(tokenString string) (*jwt.Token, error)
- Signer interface — extends Verifier; adds Sign(claims jwt.Claims) (string, error)
- signer_hmac.go — NewHMACSigner(secret) → HS256; jwt.WithJSONNumber() on Verify
- signer_rsa.go — NewRSASigner(key) + NewRSASignerFromPEM(pem) → RS256
- verifier_rsa.go — NewRSAPublicKeyVerifier + NewRSAPublicKeyVerifierFromPEM → RS256 verify-only
- signer_ec.go — NewECSigner(key) + NewECSignerFromPEM(pem) → ES256/384/512; algorithm
  auto-detected from key curve (P-256→ES256, P-384→ES384, P-521→ES512)
- verifier_ec.go — NewECPublicKeyVerifier + NewECPublicKeyVerifierFromPEM → EC verify-only

Token lifecycle:
- TokenConfig struct — AccessTTL, RefreshTTL, Issuer
- TokenPair struct — AccessToken, RefreshToken, ExpiresIn
- IssueTokenPair — access + refresh pair; customClaims merged at top level; refresh
  carries only sub/iss/iat/exp/jti/fam; jwt.WithJSONNumber() preserves int64 bitmasks
- Blacklist interface — IsRevoked + Revoke; satisfied by cache-valkey via duck typing
- ErrTokenRevoked — errors.New sentinel; errors.Is pattern for replay-attack detection
- RefreshTokenPair — verifies token, checks blacklist, revokes old JTI, issues new pair

HTTP middleware:
- AuthMiddleware(logger, verifier, publicPaths) — verifies Bearer tokens; calls
  authmw.SetTokenData on success; 401 routed through httputil.Error (Warn level);
  publicPaths use path.Match wildcards; accepts Verifier (not Signer) to enforce
  narrowest-interface principle for verify-only services

Compliance test (package authjwt_test) enforces CT-6 (≤1 exported TypeSpec/file),
compile-time interface satisfaction, and behavioural coverage: HMAC/RSA/EC sign+verify,
algorithm mismatch rejection, IssueTokenPair claims/jti/fam, RefreshTokenPair success/
revoked/blacklist-error/custom-claims, MaxInt64 json.Number precision, AuthMiddleware
valid/invalid/expired/missing/public-path/wildcard/JSON-body/RSA-verifier/SetTokenData.

Depends on auth v1.0.0, contracts v1.0.0, core v1.0.0, web v1.0.0, jwt/v5 v5.2.1.

- identifiable.go: package-level Module variable (observability.Identifiable) for version
  identification — auth-jwt is a function library; not registered with the launcher

tokens.go

@@ -0,0 +1,62 @@
+package authjwt
+
+import (
+	"crypto/rand"
+	"fmt"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+)
+
+// IssueTokenPair signs a new access + refresh token pair for uid.
+// customClaims are merged into the access token at the top level. Use this to embed
+// per-resource permission masks so ClaimsPermissionProvider can read them without a DB call.
+// The refresh token carries only sub, iss, iat, exp, jti, and fam (token family).
+func IssueTokenPair(signer Signer, uid string, customClaims map[string]any, cfg TokenConfig) (TokenPair, error) {
+	now := time.Now()
+
+	accessClaims := jwt.MapClaims{
+		"sub": uid,
+		"iss": cfg.Issuer,
+		"iat": jwt.NewNumericDate(now),
+		"exp": jwt.NewNumericDate(now.Add(cfg.AccessTTL)),
+		"jti": newJTI(),
+	}
+	for k, v := range customClaims {
+		accessClaims[k] = v
+	}
+
+	accessToken, err := signer.Sign(accessClaims)
+	if err != nil {
+		return TokenPair{}, fmt.Errorf("sign access token: %w", err)
+	}
+
+	refreshClaims := jwt.MapClaims{
+		"sub": uid,
+		"iss": cfg.Issuer,
+		"iat": jwt.NewNumericDate(now),
+		"exp": jwt.NewNumericDate(now.Add(cfg.RefreshTTL)),
+		"jti": newJTI(),
+		"fam": newJTI(),
+	}
+
+	refreshToken, err := signer.Sign(refreshClaims)
+	if err != nil {
+		return TokenPair{}, fmt.Errorf("sign refresh token: %w", err)
+	}
+
+	return TokenPair{
+		AccessToken:  accessToken,
+		RefreshToken: refreshToken,
+		ExpiresIn:    int64(cfg.AccessTTL.Seconds()),
+	}, nil
+}
+
+func newJTI() string {
+	b := make([]byte, 16)
+	_, _ = rand.Read(b)
+	b[6] = (b[6] & 0x0f) | 0x40
+	b[8] = (b[8] & 0x3f) | 0x80
+	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
+		b[0:4], b[4:6], b[6:8], b[8:10], b[10:])
+}