feat(valkey): initial stable release v0.9.0

Valkey (Redis-compatible) client component with launcher lifecycle and health check integration.

What's included:
- Config with Addrs, Password, SelectDB, CacheSizeEachConn (env-driven)
- Provider interface exposing native valkey-go Client() directly (no wrapper)
- Component interface: launcher.Component + health.Checkable + Provider
- New(logger, cfg) constructor for lifecycle registration via lc.Append
- Health check via PING at LevelDegraded priority
- Graceful shutdown calling client.Close() in OnStop

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

CHANGELOG.md

@@ -0,0 +1,29 @@
+# Changelog
+
+All notable changes to this module will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this module adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.9.0] - 2026-03-18
+
+### Added
+
+- `Config` struct — Valkey connection settings loaded from environment variables: `VK_ADDRS` (required, comma-separated server addresses), `VK_PASSWORD` (authentication password), `VK_DB` (database index, default `0`), `VK_CLIENT_CACHE_MB` (per-connection client-side cache size in MB, default `0` disables caching)
+- `Provider` interface — `Client() valkey.Client`; for consumers that only need access to the native `valkey-go` client
+- `Component` interface — embeds `launcher.Component`, `health.Checkable`, and `Provider`; the full lifecycle-managed surface registered with the launcher
+- `New(logger logz.Logger, cfg Config) Component` — constructor; returns a `Component` ready for `lc.Append`
+- `OnInit` — constructs the `valkey-go` client from `Config`; enables client-side caching when `CacheSizeEachConn > 0`
+- `OnStart` — verifies connectivity by issuing a `PING` command; returns an error if the ping fails
+- `OnStop` — calls `client.Close()` for graceful shutdown
+- `HealthCheck(ctx context.Context) error` — issues `PING`; returns an error if the client is nil or the command fails
+- `Name() string` — returns `"valkey"`
+- `Priority() health.Level` — returns `health.LevelDegraded`; a cache outage degrades service rather than halting it
+
+### Design Notes
+
+- The native `valkey-go` client is exposed directly via `Client()` with no wrapping or re-exported command subset; callers use the full command-builder API and own all serialisation and key namespacing.
+- `Provider` / `Component` split follows the framework pattern: inject `Provider` into repositories and services, inject `Component` only at the lifecycle registration site.
+- Health priority is `LevelDegraded` by design — callers must handle cache misses by falling back to the primary datastore rather than treating a Valkey outage as fatal.
+
+[0.9.0]: https://code.nochebuena.dev/go/valkey/releases/tag/v0.9.0