feat(cache-valkey): initial implementation — Provider, adapters (v1.0.0)

Introduces code.nochebuena.dev/einherjar/cache-valkey — the Valkey cache starter
for the Einherjar framework. Absorbs the valkey package from micro-lib and adds
three duck-typed adapters that wire directly into auth, web, and auth-jwt.

Core:
- Provider interface — Get, Set, Del, Exists, Expire, IncrWithTTL, Native()
- Component interface — lifecycle.Component + observability.Checkable + Provider
- Config struct (EINHERJAR_VALKEY_* env vars)
- New(logger, cfg) Component — creates valkey-go client in OnInit;
  PING in OnStart; logs "valkey: connected"
- IncrWithTTL implemented with Lua script (atomic INCR + conditional EXPIRE);
  race-free fixed-window semantics with no MULTI/EXEC overhead
- Priority: LevelDegraded — Valkey outage degrades, does not halt the service

Adapters (duck-typed — no import of auth, web, or auth-jwt):
- PermissionCache — Get/Set int64 bitmasks as string; satisfies auth/rbac.Cache
- RateLimiterStore — fixed-window via IncrWithTTL; satisfies web/mw.RateLimiterStore
- Blacklist — Exists/Set "1" with TTL; satisfies auth-jwt.Blacklist

Compliance test verifies CT-6, duck-type shape assignments, and full adapter
behavioural coverage with a mockProvider (no live server required).

- Component interface embeds observability.Identifiable; identifiable.go implements
  ModulePath and ModuleVersion via runtime/debug.ReadBuildInfo() — prints in launcher banner

provider.go

@@ -0,0 +1,30 @@
+package cachevalkey
+
+import (
+	"context"
+	"time"
+
+	vk "github.com/valkey-io/valkey-go"
+)
+
+// Provider wraps the most common Valkey operations using only standard Go types.
+// Callers that need operations beyond this interface call Native().
+// Component satisfies Provider — pass the result of New() wherever a Provider is expected.
+type Provider interface {
+	// Get retrieves the string value of key. Returns ("", false, nil) on cache miss.
+	Get(ctx context.Context, key string) (string, bool, error)
+	// Set stores value under key. Pass 0 ttl for no expiry.
+	Set(ctx context.Context, key string, value string, ttl time.Duration) error
+	// Del removes one or more keys. Silently skips non-existent keys.
+	Del(ctx context.Context, keys ...string) error
+	// Exists reports whether key is present.
+	Exists(ctx context.Context, key string) (bool, error)
+	// Expire sets a TTL on an existing key.
+	Expire(ctx context.Context, key string, ttl time.Duration) error
+	// IncrWithTTL atomically increments the integer counter at key and sets
+	// its expiry on first increment. Returns the new counter value.
+	// If key does not exist it is created with value 1.
+	IncrWithTTL(ctx context.Context, key string, ttl time.Duration) (int64, error)
+	// Native returns the underlying valkey-go client for operations not in Provider.
+	Native() vk.Client
+}