Queue remote reply scraping

Persisting remote posts now records replies collections as background
scrape jobs instead of fetching and walking them synchronously.  The job
state is stored in PostgreSQL with per-origin tracking so worker nodes can
process it later.

Fixes #445

Assisted-by: Codex:gpt-5.5

Author: dahlia

drizzle/0082_remote_reply_scrape_jobs.sql

@@ -0,0 +1,35 @@
+CREATE TYPE "public"."remote_reply_scrape_job_status" AS ENUM('pending', 'processing', 'completed', 'failed');--> statement-breakpoint
+CREATE TABLE "remote_reply_scrape_jobs" (
+	"id" uuid PRIMARY KEY NOT NULL,
+	"post_id" uuid NOT NULL,
+	"post_iri" text NOT NULL,
+	"replies_iri" text NOT NULL,
+	"base_url" text NOT NULL,
+	"origin_host" text NOT NULL,
+	"depth" integer DEFAULT 0 NOT NULL,
+	"status" "remote_reply_scrape_job_status" DEFAULT 'pending' NOT NULL,
+	"attempts" integer DEFAULT 0 NOT NULL,
+	"fetched_items" integer DEFAULT 0 NOT NULL,
+	"next_attempt_at" timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+	"error_message" text,
+	"created" timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+	"started_at" timestamp with time zone,
+	"completed_at" timestamp with time zone,
+	"updated" timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+	CONSTRAINT "remote_reply_scrape_jobs_replies_iri_unique" UNIQUE("replies_iri")
+);
+--> statement-breakpoint
+CREATE TABLE "remote_reply_scrape_origins" (
+	"origin_host" text PRIMARY KEY NOT NULL,
+	"next_request_at" timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+	"last_request_at" timestamp with time zone,
+	"processing_job_id" uuid,
+	"processing_started_at" timestamp with time zone,
+	"updated" timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "remote_reply_scrape_jobs" ADD CONSTRAINT "remote_reply_scrape_jobs_post_id_posts_id_fk" FOREIGN KEY ("post_id") REFERENCES "public"."posts"("id") ON DELETE cascade ON UPDATE no action;--> statement-breakpoint
+CREATE INDEX "remote_reply_scrape_jobs_status_next_attempt_at_index" ON "remote_reply_scrape_jobs" USING btree ("status","next_attempt_at");--> statement-breakpoint
+CREATE INDEX "remote_reply_scrape_jobs_origin_host_status_next_attempt_at_index" ON "remote_reply_scrape_jobs" USING btree ("origin_host","status","next_attempt_at");--> statement-breakpoint
+CREATE INDEX "remote_reply_scrape_origins_next_request_at_index" ON "remote_reply_scrape_origins" USING btree ("next_request_at");--> statement-breakpoint
+CREATE INDEX "remote_reply_scrape_origins_processing_job_id_index" ON "remote_reply_scrape_origins" USING btree ("processing_job_id");