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

tests/test_telemetry.py

@@ -83,7 +83,6 @@ class TestTelemetryEnabled:
             mock_at = MagicMock()
             with patch.object(telemetry_module, "_oss_telemetry_instance", mock_at):
                 mock_memory = MagicMock()
-                mock_memory.config.graph_store.config = None
                 mock_memory.api_version = "v1"
                 telemetry_module.capture_event("test.event", mock_memory)
                 mock_at.capture_event.assert_called_once()
@@ -223,7 +222,6 @@ class TestTelemetrySingleton:
                 with patch("mem0.memory.telemetry.get_or_create_user_id", return_value="u"):
                     with patch("atexit.register"):
                         mock_memory = MagicMock()
-                        mock_memory.config.graph_store.config = None
                         mock_memory.api_version = "v1"
 
                         telemetry_module.capture_event("e1", mock_memory)
@@ -242,7 +240,6 @@ class TestTelemetrySingleton:
                 with patch("mem0.memory.telemetry.get_or_create_user_id", return_value="u"):
                     with patch("atexit.register"):
                         mock_memory = MagicMock()
-                        mock_memory.config.graph_store.config = None
                         mock_memory.api_version = "v1"
 
                         for i in range(50):
@@ -421,7 +418,6 @@ class TestTelemetryNullUserIdHandling:
 
             with patch.object(telemetry_module, "_oss_telemetry_instance", mock_at):
                 mock_memory = MagicMock()
-                mock_memory.config.graph_store.config = None
                 mock_memory.api_version = "v1"
 
                 # This should not raise, even when telemetry fails