feat(server): meter AI point usage across tenant AI features

Adds an ai_point_usage_logs ledger and a reserve/refund/complete pipeline
that charges AI points for article selection optimize, template analyze
/title/outline, and KOL prompt generate/optimize. Pending reservations
are reconciled when the kol-assist worker and template-assist tasks
finish or fail, so points refund automatically on errors. Workspace now
exposes the AI quota status and a paginated usage ledger.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/migrations/20260428110000_create_ai_point_usage_logs.down.sql

@@ -0,0 +1,3 @@
+DROP INDEX IF EXISTS idx_quota_reservations_tenant_type_created_status;
+
+DROP TABLE IF EXISTS ai_point_usage_logs;

server/migrations/20260428110000_create_ai_point_usage_logs.up.sql

@@ -0,0 +1,37 @@
+CREATE TABLE ai_point_usage_logs (
+    id                       BIGSERIAL PRIMARY KEY,
+    tenant_id                BIGINT NOT NULL REFERENCES tenants(id),
+    operator_id              BIGINT REFERENCES users(id),
+    quota_reservation_id     BIGINT REFERENCES quota_reservations(id),
+    usage_type               VARCHAR(64) NOT NULL,
+    resource_type            VARCHAR(64),
+    resource_id              BIGINT,
+    resource_uid             VARCHAR(128),
+    request_chars            INT NOT NULL DEFAULT 0,
+    base_chars               INT NOT NULL DEFAULT 1000,
+    points                   INT NOT NULL,
+    status                   VARCHAR(20) NOT NULL DEFAULT 'pending',
+    model                    VARCHAR(128),
+    metadata_json            JSONB NOT NULL DEFAULT '{}'::jsonb,
+    error_message            TEXT,
+    completed_at             TIMESTAMPTZ,
+    created_at               TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at               TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    CONSTRAINT chk_ai_point_usage_status
+        CHECK (status IN ('pending', 'completed', 'refunded', 'failed'))
+);
+
+CREATE INDEX idx_ai_point_usage_tenant_created
+    ON ai_point_usage_logs(tenant_id, created_at DESC);
+
+CREATE INDEX idx_ai_point_usage_tenant_operator_created
+    ON ai_point_usage_logs(tenant_id, operator_id, created_at DESC);
+
+CREATE INDEX idx_ai_point_usage_reservation
+    ON ai_point_usage_logs(quota_reservation_id);
+
+CREATE INDEX idx_ai_point_usage_resource
+    ON ai_point_usage_logs(tenant_id, resource_type, resource_id, resource_uid);
+
+CREATE INDEX idx_quota_reservations_tenant_type_created_status
+    ON quota_reservations(tenant_id, quota_type, created_at, status);