docs: refresh references stale since the v3 pipeline landed

Commit a488e1904 deleted mem0/graphs/ and mem0-ts/src/oss/src/graphs/ when the
v3 pipeline landed, and 3f717e545 reframed the docs as Platform-only, but the
agent-facing context files were never updated. Agents reading them still
believe OSS graph memory exists and propose graph_store config that cannot work.

- AGENTS.md: drop graphs/ from the directory map and dependency tree, correct
  the provider table (4 categories, not 5; LLMs 24->18, vector stores 30->25,
  embeddings 15->12), and rewrite the Graph Memory section as Platform-only
- skills: replace the OSS graph-memory prompt example and stop indexing
  /open-source/features/graph-memory, which 404s; also fix four other
  SECTION_MAP paths that no longer resolve
- mem0/exceptions.py: DependencyError example referenced kuzu/graph_store
- tests/test_telemetry.py: drop four mock_memory.config.graph_store lines;
  graph_store is not a MemoryConfig field and telemetry never reads it
- CONTRIBUTING.md: add the three missing release tag prefixes (opencode-v*,
  pi-agent-v*, n8n-nodes-mem0-v*) and note Zapier deploys off-registry

CONTRIBUTING.md

@@ -161,6 +161,13 @@ is created with the correct tag prefix.
 | `@mem0/cli` (Node CLI) | npm | `cli-node-v*` | `cli-node-v0.1.2` |
 | `@mem0/vercel-ai-provider` | npm | `vercel-ai-v*` | `vercel-ai-v2.0.6` |
 | `@mem0/openclaw-mem0` | npm | `openclaw-v*` | `openclaw-v1.0.1` |
+| `@mem0/opencode-plugin` | npm | `opencode-v*` | `opencode-v1.0.1` |
+| `@mem0/pi-agent-plugin` | npm | `pi-agent-v*` | `pi-agent-v1.0.1` |
+| `@mem0/n8n-nodes-mem0` | npm | `n8n-nodes-mem0-v*` | `n8n-nodes-mem0-v1.0.1` |
+
+The Zapier app (`integrations/zapier-mem0`) deploys to Zapier's own platform rather
+than a package registry, so it has no release tag. Deploy it manually with
+`gh workflow run zapier-mem0-cd.yml --ref main`.
 
 ### How to Release