docs: document model cache + log paths and sandbox guidance in Storage (#100)

PR #101 patched the pre-rework README; this adds the missing persistent paths
(embedding model cache ~/.local/share/cortexkit/magic-context/models, the temp
log) plus Docker/CI/sandbox guidance (persist the storage dir; disable local
embeddings to skip the ~90MB model download) to the current README.

Co-authored-by: Alfonso [Magic Context] <288211368+alfonso-magic-context@users.noreply.github.com>

Author: ualtinok

README.md

@@ -244,6 +244,16 @@ Settings live in `magic-context.jsonc`. Everything has sensible defaults; projec
 
 All durable state lives in a local SQLite database under the shared CortexKit store (`~/.local/share/cortexkit/magic-context/context.db`, XDG-equivalent on Windows; legacy OpenCode-folder databases are migrated forward on first boot). If the database can't be opened, Magic Context disables itself and notifies you. Memories are keyed to a **stable project identity** derived from the repo, so they follow a project across worktrees, clones, and forks rather than being tied to a directory path.
 
+Magic Context also writes to a few other locations:
+
+| Path | What | Persistence |
+|---|---|---|
+| `~/.local/share/cortexkit/magic-context/context.db` | SQLite database — tags, compartments, memories, all durable state (XDG-equivalent on Windows) | **Must persist.** Losing it loses your memory/history. |
+| `~/.local/share/cortexkit/magic-context/models/` | Local embedding model cache (~90 MB `Xenova/all-MiniLM-L6-v2` ONNX), downloaded on first use when local embeddings are enabled | Should persist, else re-downloaded each run. Not used when `memory.enabled: false` or an `openai_compatible`/`ollama` embedding backend is configured. |
+| `${TMPDIR}/opencode/magic-context/magic-context.log` (`pi/` for Pi) | Diagnostic log | Disposable. |
+
+**Sandboxed / ephemeral environments (Docker, CI, disposable containers):** mount the `~/.local/share/cortexkit/magic-context/` directory on a persistent volume so the database and model cache survive between runs. If only the model cache is ephemeral, the model is simply re-downloaded; if the database is ephemeral, memory and history don't accumulate. To avoid the ~90 MB model download entirely, set `memory.enabled: false` or point `embedding` at a remote `openai_compatible`/`ollama` backend.
+
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