feat(scripts): fold model downloads into update.sh, skip if already present

Today's embedding-server crash-loop (missing nomic-embed-text GGUF) was a
manual step nobody ran. update.sh now runs both downloader profiles
itself, every time, before bringing services up -- no separate command to
remember.

- docker-compose.yml: downloader/downloader-embedding commands gain a
  `test -f ... && skip || curl ...` guard, so re-running update.sh never
  re-downloads an existing model file.
- scripts/update.sh: runs both profiles after image pull/build, before
  service recreation.
- scripts/download-model.sh removed -- folded in, redundant standalone
  script.
- README.md / docs/memory-knowledgebase.md updated accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018WHfjWrSEcGhCoeu6dQfDa

docker-compose.yml

@@ -66,8 +66,10 @@ services:
     networks: [ai-stack]
 
   # ponytail: one-off downloader, not a standing service — run via
-  # `docker compose --profile tools run --rm downloader` (see scripts/download-model.sh).
-  # Keeps the model file inside the named `models` volume instead of a host bind-mount.
+  # `docker compose --profile tools run --rm downloader`. Folded into
+  # scripts/update.sh, which runs this every time; the `test -f` guard is
+  # what makes that safe to re-run without re-downloading. Keeps the model
+  # file inside the named `models` volume instead of a host bind-mount.
   downloader:
     image: curlimages/curl:latest
     profiles: ["tools"]
@@ -79,11 +81,14 @@ services:
     entrypoint: ["sh", "-c"]
     command:
       - >
+        test -f /models/${LLAMA_MODEL_FILE:-Qwen3.8-27B-UD-Q4_K_XL.gguf} &&
+        echo "already downloaded, skipping" ||
         curl -L --fail --create-dirs -o /models/${LLAMA_MODEL_FILE:-Qwen3.8-27B-UD-Q4_K_XL.gguf}
         https://huggingface.co/unsloth/Qwen3.8-27B-GGUF/resolve/main/${LLAMA_MODEL_FILE:-Qwen3.8-27B-UD-Q4_K_XL.gguf}
 
   # ponytail: same one-off pattern as `downloader`, for the embedding model —
-  # run via `docker compose --profile tools run --rm downloader-embedding`.
+  # run via `docker compose --profile tools run --rm downloader-embedding`,
+  # also folded into scripts/update.sh.
   downloader-embedding:
     image: curlimages/curl:latest
     profiles: ["tools"]
@@ -93,6 +98,8 @@ services:
     entrypoint: ["sh", "-c"]
     command:
       - >
+        test -f /models/${EMBEDDING_MODEL_FILE:-nomic-embed-text-v1.5.Q8_0.gguf} &&
+        echo "already downloaded, skipping" ||
         curl -L --fail --create-dirs -o /models/${EMBEDDING_MODEL_FILE:-nomic-embed-text-v1.5.Q8_0.gguf}
         https://huggingface.co/nomic-ai/nomic-embed-text-v1.5-GGUF/resolve/main/${EMBEDDING_MODEL_FILE:-nomic-embed-text-v1.5.Q8_0.gguf}