agents: extract shared run_one_agent, standardize output formats

Three places duplicated the agent execution loop (build prompt → call
LLM → store output → parse actions → record visits): consolidate.rs,
knowledge.rs, and daemon.rs. Extract into run_one_agent() in
knowledge.rs that all three now call.

Also standardize consolidation agent prompts to use WRITE_NODE/LINK/REFINE
— the same commands the parser handles. Previously agents output
CATEGORIZE/NOTE/EXTRACT/DIGEST/DIFFERENTIATE/MERGE/COMPRESS which were
silently dropped after the second-LLM-call removal.

poc-memory/agents/separator.agent

@@ -31,25 +31,22 @@ You're given pairs of nodes that have:
 
 ## What to output
 
+For **genuine duplicates**, merge by refining the surviving node:
 ```
-DIFFERENTIATE key1 key2 "what makes them distinct"
+REFINE surviving_key
+[merged content from both nodes]
+END_REFINE
 ```
 
+For **near-duplicates that should stay separate**, add distinguishing links:
 ```
-MERGE key1 key2 "merged summary"
+LINK key1 distinguishing_context_key
+LINK key2 different_context_key
 ```
 
+For **supersession**, link them and let the older one decay:
 ```
-LINK key1 distinguishing_context_key [strength]
-LINK key2 different_context_key [strength]
-```
-
-```
-CATEGORIZE key category
-```
-
-```
-NOTE "observation"
+LINK newer_key older_key
 ```
 
 ## Guidelines