Add the harness, envs, per-bot models and chat attachments

- Harness: providers, model catalog synced hourly, automatic free picks,
  cooldowns, tool loop with context trimming, MCP computer tools
- Bots queue runs replies and tasks through the harness; jobs wait
  (attempt refunded) while every model is resting
- Envs: Settings > Environment, scoped general/workspace/computer,
  written to computers and redacted from tool output
- Models: Settings > Models, per-harness provider select defaulting to
  OpenRouter, and a models modal on each bot's chat (the coordinator's
  edits the defaults)
- Chat: thinking row while a reply runs, file attachments (upload,
  paste, drop) that replies read as images, audio and document text
- Fix media uploads failing after a user's first file, and private
  files being served from the public media path

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/backend/db/harness/grab-default-harness-provider-id.ts

@@ -0,0 +1,19 @@
+import BunSQLite from "@moduletrace/bun-sqlite";
+import type { BUN_SQLITE_COBBLE_HARNESS_PROVIDERS } from "@/db/types/db";
+import { DefaultHarnessProviderKind } from "@/src/dict/harness-provider-dict";
+
+/**
+ * The default provider (`DefaultHarnessProviderKind`, OpenRouter): the
+ * oldest enabled one of that kind. Undefined once it's removed or turned
+ * off, which leaves harnesses on any provider.
+ */
+export default async function grabDefaultHarnessProviderId() {
+    const row = (
+        await BunSQLite.sql<BUN_SQLITE_COBBLE_HARNESS_PROVIDERS>({
+            sql: `SELECT id FROM harness_providers WHERE kind = ? AND enabled = 1 ORDER BY id ASC LIMIT 1`,
+            values: [DefaultHarnessProviderKind],
+        })
+    ).payload?.[0];
+
+    return row?.id || undefined;
+}