plugin-catalog: add memobase memory provider

Self-hosted Memobase (user profile + event timeline) as a MemoryProvider.
Hybrid BM25 + vector + entity RRF recall, temporal boost on time-window
queries, and a conditional cross-encoder rerank.

The reranker is opt-in with no default endpoint: it runs only when the
deployment sets both rerank_base_url and rerank_api_key, so a default
install talks only to the user's own Memobase server.

Pinned to 4e8e447 of fred0m/hermes-memobase-provider. Declares the two env
vars the install must prompt for.

plugin-catalog/memobase.yaml

@@ -0,0 +1,16 @@
+name: memobase
+repo: https://github.com/fred0m/hermes-memobase-provider
+sha: 4e8e447966acefaea372395e2db96ca0d0127f18
+description: Memobase memory provider — self-hosted user profile + event timeline
+  recall, with hybrid BM25/vector/entity retrieval and automatic per-turn prefetch.
+maintainer: fred0m
+tier: community
+category: memory
+docs_url: https://github.com/fred0m/hermes-memobase-provider#readme
+capabilities:
+  provides_tools: []
+  provides_hooks: []
+  provides_middleware: []
+  requires_env:
+  - MEMOBASE_API_KEY
+  - MEMOBASE_BASE_URL