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

rate_limiter_store.go

@@ -0,0 +1,42 @@
+package cachevalkey
+
+import (
+	"context"
+	"time"
+)
+
+// rateLimiterStoreShape mirrors web/mw.RateLimiterStore for compile-time duck-type verification.
+// Cache-valkey must not import web (D-1), so the shape is defined locally.
+type rateLimiterStoreShape interface {
+	Allow(ctx context.Context, key string) (bool, error)
+}
+
+var _ rateLimiterStoreShape = (*RateLimiterStore)(nil)
+
+// RateLimiterStore is a Valkey-backed fixed-window rate limiter.
+// Satisfies web/mw.RateLimiterStore via duck typing — no import of that package required.
+//
+// window is the length of the time window; limit is the maximum number of requests
+// allowed within that window. When the store is temporarily unavailable, Allow returns
+// (false, err); the web middleware fails open on non-nil errors.
+type RateLimiterStore struct {
+	provider Provider
+	window   time.Duration
+	limit    int64
+}
+
+// NewRateLimiterStore returns a RateLimiterStore backed by p.
+// window is the rate limit window; limit is the maximum requests per window.
+func NewRateLimiterStore(p Provider, window time.Duration, limit int64) *RateLimiterStore {
+	return &RateLimiterStore{provider: p, window: window, limit: limit}
+}
+
+// Allow reports whether the request identified by key is within the rate limit.
+// Uses a fixed-window counter stored in Valkey (atomically via Lua).
+func (s *RateLimiterStore) Allow(ctx context.Context, key string) (bool, error) {
+	count, err := s.provider.IncrWithTTL(ctx, key, s.window)
+	if err != nil {
+		return false, err
+	}
+	return count <= s.limit, nil
+}