feat(agents): agent seats - per-agent SOUL, role, definitions dir (#36)

- agents/<name>/ holds agent.json (strictly validated: version, name,
  role?, capabilities?, workspace?, session?) + SOUL.md (persona prose)
- agent.sh: definition loading (quote-safe node defaults file), runtime
  SOUL copy to dataRoot/agents/<name>/, MOSAIC_AGENT_SOUL_FILE ->
  loader fills the SOUL slot from the seat's persona (contract SOUL =
  default persona; governance never overridden)
- seat.json written once at instantiation (seatVersion, name, role, at)
- identity section gains agent role; compose passthrough for role+SOUL
- live user context (M14) + seat SOUL compose the full persona:
  governance -> persona -> identity -> user -> mission
- RELEASE -> 0.0.10; packaged and health-gated activated
- example seat committed: agents/researcher

Closes #36

scripts/test-task.sh

@@ -236,6 +236,17 @@ EOF
     printf '{"missionVersion":1,"id":"m-pol","objective":"o","capabilities":{"tools":["sudo"]}}' > "$SANDBOX/pol-m.json"
     expect_exit "invalid mission capabilities rejected" 2 -- \
         env MOSAIC_CONFIG="$SANDBOX/mock-adapters.json" $TASK validate "$SANDBOX/pol-t.json"
+
+    # live user context (M14): dispatched to every launch without rebuild
+    mkdir -p "$SANDBOX/data/user"
+    printf '\nUSER-CANON-MARKER\n' >> "$SANDBOX/data/user/USER.md"
+    expect_exit "task run with user layer present" 0 -- \
+        env MOSAIC_CONFIG="$SANDBOX/mock-adapters.json" MOSAIC_MOCK_RESPONSE=MOSAIC_HELLO_OK \
+        scripts/run-task.sh run "$SANDBOX/ok.json"
+    grep -q 'USER CONTEXT: USER.md' "$SANDBOX/data/system-prompt.md" \
+        && grep -q 'USER-CANON-MARKER' "$SANDBOX/data/system-prompt.md" \
+        && check "user context dispatched into generated prompt" 0 \
+        || check "user context dispatched into generated prompt" 1
 else
     echo "skip adapter seam cases (docker daemon unavailable)"
 fi