feat: v0.4.0 — File sharing + multi-target messages

Files: MinIO-backed file sharing built into the broker.
share_file for persistent mesh files, send_message(file:) for
ephemeral attachments. Presigned URLs for download, access
tracking per peer.

Broker infra: MinIO in docker-compose, internal network.
HTTP POST /upload endpoint. WS handlers for get_file,
list_files, file_status, delete_file.

Multi-target: send_message(to:) accepts string or array.
Targets deduplicated before delivery.

Targeted views: MCP instructions teach Claude to send
tailored messages per audience instead of generic broadcasts.

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

packages/db/migrations/0009_add-file-tables.sql

@@ -0,0 +1,28 @@
+CREATE TABLE "mesh"."file" (
+	"id" text PRIMARY KEY NOT NULL,
+	"mesh_id" text NOT NULL,
+	"name" text NOT NULL,
+	"size_bytes" integer NOT NULL,
+	"mime_type" text,
+	"minio_key" text NOT NULL,
+	"tags" text[] DEFAULT '{}',
+	"persistent" boolean DEFAULT true NOT NULL,
+	"uploaded_by_name" text,
+	"uploaded_by_member" text,
+	"target_spec" text,
+	"uploaded_at" timestamp DEFAULT now() NOT NULL,
+	"expires_at" timestamp,
+	"deleted_at" timestamp
+);
+--> statement-breakpoint
+CREATE TABLE "mesh"."file_access" (
+	"id" text PRIMARY KEY NOT NULL,
+	"file_id" text NOT NULL,
+	"peer_session_pubkey" text,
+	"peer_name" text,
+	"accessed_at" timestamp DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+ALTER TABLE "mesh"."file" ADD CONSTRAINT "file_mesh_id_mesh_id_fk" FOREIGN KEY ("mesh_id") REFERENCES "mesh"."mesh"("id") ON DELETE cascade ON UPDATE cascade;--> statement-breakpoint
+ALTER TABLE "mesh"."file" ADD CONSTRAINT "file_uploaded_by_member_member_id_fk" FOREIGN KEY ("uploaded_by_member") REFERENCES "mesh"."member"("id") ON DELETE no action ON UPDATE no action;--> statement-breakpoint
+ALTER TABLE "mesh"."file_access" ADD CONSTRAINT "file_access_file_id_file_id_fk" FOREIGN KEY ("file_id") REFERENCES "mesh"."file"("id") ON DELETE cascade ON UPDATE no action;