fix: resolve 4 unhealthy services from fresh volume rebuild

- router-gateway: sync 10 missing jobengine routes to local config (prevent array merge bleed-through)
- findings-ledger-web: add VulnExplorer tables to postgres-init bootstrap script
- timeline-web: replace competing migration hosted service with standard AddStartupMigrations
- graph-api: handle null PostgresGraphRepository gracefully, add graph schema to init
- scheduler-web: add failure_signatures table to init bootstrap

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

devops/compose/postgres-init/03-scheduler-tables.sql

@@ -690,3 +690,26 @@ ALTER TABLE scheduler.scheduler_exceptions FORCE ROW LEVEL SECURITY;
 CREATE POLICY scheduler_exceptions_tenant_isolation ON scheduler.scheduler_exceptions FOR ALL
     USING (tenant_id = scheduler_app.require_current_tenant())
     WITH CHECK (tenant_id = scheduler_app.require_current_tenant());
+
+-- ============================================================================
+-- failure_signatures - Scheduler failure signature tracking
+-- ============================================================================
+
+CREATE TABLE IF NOT EXISTS scheduler.failure_signatures (
+    signature_id   UUID        NOT NULL,
+    tenant_id      TEXT        NOT NULL,
+    signature_key  TEXT        NOT NULL,
+    pattern        TEXT        NOT NULL,
+    severity       TEXT        NOT NULL DEFAULT 'medium',
+    description    TEXT,
+    remediation    TEXT,
+    auto_retry     BOOLEAN     NOT NULL DEFAULT false,
+    max_retries    INT         NOT NULL DEFAULT 0,
+    created_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    created_by     TEXT,
+    CONSTRAINT failure_signatures_pkey PRIMARY KEY (signature_id)
+);
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_scheduler_failure_signatures_key
+    ON scheduler.failure_signatures(tenant_id, signature_key);