provenance: set POC_PROVENANCE for agent subprocesses, Jaccard initial strength

Agent subprocess calls now set POC_PROVENANCE=agent:{name} so any
nodes/links created via tool calls are tagged with the creating agent.
This makes agent transcripts indistinguishable from conscious sessions
in format — important for future model training.

new_relation() now reads POC_PROVENANCE env var directly (raw string,
not enum) since agent names are dynamic.

link-add now computes initial strength from Jaccard similarity instead
of hardcoded 0.8. New links start at a strength reflecting actual
neighborhood overlap.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/src/agents/llm.rs

@@ -93,6 +93,9 @@ fn call_model_with_tools(agent: &str, model: &str, prompt: &str,
     // Tell hooks this is a daemon agent call, not interactive
     cmd.env("POC_AGENT", "1");
 
+    // Set provenance so any nodes/links created by tool calls are tagged
+    cmd.env("POC_PROVENANCE", format!("agent:{}", agent));
+
     let start = std::time::Instant::now();
 
     let mut child = unsafe {