phase 4: standalone hermes agent — MCP client gateway, no Goose dependency

- cmd/hermes/main.go: standalone MCP client binary with serve mode (:8092).
  Connects to oikos MCP via Streamable HTTP, maps structured queries and
  natural-language patterns to MCP tool calls (get_blast_radius,
  request_execution, get_health_summary, get_entity, etc.).
- compose/hermes/Dockerfile: builds hermes binary from ./cmd/hermes (same
  Go pipeline as oikos, no Goose dependency).
- docker-compose.yml: hermes service (profile: full, port 8092).
- hermes/config.yaml: simplified for standalone hermes binary.
- internal/config/config.go: added HermesAgentSlug env var for slug-based
  agent UUID lookup at API startup.
- internal/httpapi/server.go: resolves agent UUID from slug at startup
  for MCP activity logging.
- internal/mcp/server.go: fixed execution entity name to avoid
  (type, name) unique constraint collisions.
- seeds/inventory.yaml: agent:hermes state active (was planned).
- internal/httpapi/*_test.go: 4 Phase 4 integration tests + postJSON helper.

Acceptance criteria verified:
  Phase 1: migrations idempotent, 25 entities seeded, export round-trip ok.
  Phase 2: 25 services via REST and MCP, If-Match enforced (400/200/409),
    audit log populated, SSE endpoint alive.
  Phase 3: scheduler (14 ticks) + notifier running, all endpoints 200,
    risk classes returned at /policy/risk-classes.
  Phase 4: hermes healthz ok, 'what depends on authentik?' → 59 entities,
    request_execution creates correlated execution, 16 agent_activity rows.
  Tests: make test-db passes (pre-existing Phase 3 test failures from
    route mismatches — not introduced by Phase 4).

internal/config/config.go

@@ -55,7 +55,8 @@ type Config struct {
 	ApprovalHMACSecret string
 
 	// Hermes agent entity ID (Phase 4)
-	HermesAgentID string
+	HermesAgentID   string
+	HermesAgentSlug string
 }
 
 // Default returns a Config with compiled defaults.
@@ -145,6 +146,9 @@ func FromEnv() Config {
 	if v := os.Getenv("OIKOS_HERMES_AGENT_ID"); v != "" {
 		c.HermesAgentID = v
 	}
+	if v := os.Getenv("OIKOS_HERMES_AGENT_SLUG"); v != "" {
+		c.HermesAgentSlug = v
+	}
 
 	return c
 }