Use Valkey instead of Redis

Redis 7.4+ is RSALv2/SSPL and 8.0+ adds AGPLv3, none of which a
closed-source commercial product can ship. Valkey is BSD-3-Clause and
speaks the same RESP protocol, so the `redis` crate works unchanged -
`CONTINUUM_REDIS_URL` becomes `CONTINUUM_VALKEY_URL`, `Config.redis_url`
becomes `valkey_url`, and `Reporter`'s connection field follows.

The `redis://` scheme and the `redis` crate itself deliberately stay:
both name the RESP wire protocol rather than the server we deploy, and
redis-rs has no `valkey://` scheme to use instead. Commented in place so
the inconsistency reads as intentional.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/config.rs

@@ -2,7 +2,7 @@ use std::env;
 
 #[derive(Debug, Clone)]
 pub struct Config {
-    pub redis_url: String,
+    pub valkey_url: String,
     pub frame_stream: String,
     pub consumer_group: String,
     pub consumer_name: String,
@@ -11,7 +11,7 @@ pub struct Config {
 impl Config {
     pub fn from_env() -> anyhow::Result<Self> {
         Ok(Self {
-            redis_url: env_or("CONTINUUM_REDIS_URL", "redis://localhost:6379"),
+            valkey_url: env_or("CONTINUUM_VALKEY_URL", "redis://localhost:6379"),
             frame_stream: env_or("CONTINUUM_FRAME_STREAM", "stream:camera_frames"),
             consumer_group: env_or("CONTINUUM_CONSUMER_GROUP", "ai-worker"),
             consumer_name: env_or("CONTINUUM_CONSUMER_NAME", "ai-worker-1"),