fix(R6): fall back to interaction.project when LLM returns empty

Codex R6: the LLM extractor accepted the model's project field
verbatim. When the model returned empty string, clearly p06 memories
got promoted as project='', making them invisible to the p06
project-memory band and explaining the p06-offline-design harness
failure.

Fix: if model returns empty project but interaction.project is set,
inherit the interaction's project. Model-supplied project still takes
precedence when non-empty.

Two new tests lock the fallback and precedence behaviors.
R5 acknowledged (LLM extractor not yet wired into API — next task).

Test count: 278 -> 280. Harness re-run pending after deploy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/memory/extractor_llm.py

@@ -256,6 +256,8 @@ def _parse_candidates(raw_output: str, interaction: Interaction) -> list[MemoryC
         mem_type = str(item.get("type") or "").strip().lower()
         content = str(item.get("content") or "").strip()
         project = str(item.get("project") or "").strip()
+        if not project and interaction.project:
+            project = interaction.project
         confidence_raw = item.get("confidence", 0.5)
         if mem_type not in MEMORY_TYPES:
             continue