feat(fleet): add service type enum and infra scope

Replace the free-form service_type string with a ServiceType enum (ccms,
ccmc, ccb, cces, ccsa, ccnc, ccem). The short code is the canonical value
stored in the DB, the config-tree directory name and a NATS discovery
subject token; Description() gives the human-readable name.

Add a second scope alongside per-node agents: ScopeInfra covers
cluster-independent monitoring infrastructure services, which are
identified by (hostname, service_type) and carry an empty cluster.
InfraRegistry is the ScopeInfra sibling of Registry and shares the same
table, state machine and config-revision handshake. It deliberately
exposes no StartSweep: MarkStale ages rows by last_heartbeat regardless
of scope, so a single sweep goroutine per process covers both scopes.

On the repository side ServiceDB gains a Scope column and the two
queries the discovery publisher and infra enumeration need, ListActive()
and ListByScope(). ResetConnection() now also resets the fleet
repository singleton so tests get a fresh handle.

Migration 13 is edited in place rather than superseded by a new
migration: the service table is unreleased, so no existing deployment
has it yet.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/repository/migrations/sqlite3/13_add-service-table.up.sql

@@ -4,6 +4,8 @@ CREATE TABLE "service" (
     hostname VARCHAR(255) NOT NULL,
     service_type VARCHAR(255) NOT NULL,
     instance_id VARCHAR(64) NOT NULL,
+    scope VARCHAR(32) NOT NULL DEFAULT 'cluster'
+        CHECK (scope IN ('cluster', 'infra')),
     state VARCHAR(32) NOT NULL DEFAULT 'pending'
         CHECK (state IN ('pending', 'active', 'stale', 'deregistered')),
     registered_at INTEGER NOT NULL,
@@ -15,6 +17,7 @@ CREATE TABLE "service" (
 );
 
 CREATE INDEX IF NOT EXISTS services_cluster ON service (cluster);
+CREATE INDEX IF NOT EXISTS services_scope ON service (scope);
 CREATE INDEX IF NOT EXISTS services_state_heartbeat ON service (state, last_heartbeat);
 
 PRAGMA optimize;