feat(sdk-csharp): complete C# SDK feature parity with all memory API endpoints

[oxoxDev]

Summary

• Migrate all endpoint paths from /v1/memory/... to /memory/...
• Add X-Model-Id header (default: neocortex-mk1) and 3-arg constructor for custom model IDs
• Add HTTP GET and DELETE support (GetAsync, DeleteAsync, BuildQueryString)
• Add 14 new endpoints: chat, interactions, advanced recall, documents, admin & utility
• Update target framework from net8.0 to net10.0
• Update example, README, and integration test to cover all 19 methods

New Endpoints

Method	HTTP	Path
ChatMemoryAsync	POST	/memory/chat
ChatMemoryContextAsync	POST	/memory/conversations
InteractMemoryAsync	POST	/memory/interact
RecordInteractionsAsync	POST	/memory/interactions
RecallThoughtsAsync	POST	/memory/memories/thoughts
QueryMemoryContextAsync	POST	/memory/queries
InsertDocumentAsync	POST	/memory/documents
InsertDocumentsBatchAsync	POST	/memory/documents/batch
ListDocumentsAsync	GET	/memory/documents
GetDocumentAsync	GET	/memory/documents/{id}
DeleteDocumentAsync	DELETE	/memory/documents/{id}
GetGraphSnapshotAsync	GET	/memory/admin/graph-snapshot
GetIngestionJobAsync	GET	/memory/ingestion/jobs/{id}
WaitForIngestionJobAsync	—	Polling loop

Test Plan

• 50 unit tests passing (path assertions, body shape, validation, HTTP methods, polling)
• Integration test against staging (blocked locally by .NET 10 + macOS TLS 1.3 incompatibility with staging server — will pass on Linux CI or .NET 8)