fix(db): rename pgSchema exports to prevent barrel collision

chat/image/mesh modules all exported a generic `const schema`
binding. When packages/db/src/schema/index.ts did `export * from
"./chat"` + `export * from "./image"` + `export * from "./mesh"`,
TypeScript's ambiguous-re-export rule silently dropped the colliding
bindings — drizzle-kit's introspection could not find the pgSchema
instances, so CREATE SCHEMA statements were never emitted. The
migration worked on the prior dev DB only because chat/image already
existed from an earlier turbostarter run; a fresh clone would fail.

pdf.ts already used `pdfSchema` (unique name). Applied the same
pattern everywhere:
- chat.ts:  `export const chatSchema = pgSchema("chat")`
- image.ts: `export const imageSchema = pgSchema("image")`
- mesh.ts:  `export const meshSchema = pgSchema("mesh")`

Also added `CREATE EXTENSION IF NOT EXISTS vector` at the top of the
migration (pgvector is used by pdf.embedding — the generated
migration assumed it was pre-enabled).

Verified end-to-end against a fresh pgvector/pgvector:pg17 container:
`pnpm drizzle-kit migrate` applies cleanly from scratch, all 7 mesh.*
tables + chat/image/pdf/mesh schemas created correctly.

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

packages/db/migrations/0000_living_namora.sql

@@ -1,5 +1,12 @@
+CREATE EXTENSION IF NOT EXISTS vector;--> statement-breakpoint
+CREATE SCHEMA "chat";
+--> statement-breakpoint
 CREATE SCHEMA "pdf";
 --> statement-breakpoint
+CREATE SCHEMA "image";
+--> statement-breakpoint
+CREATE SCHEMA "mesh";
+--> statement-breakpoint
 CREATE TYPE "public"."credit_transaction_type" AS ENUM('signup', 'purchase', 'usage', 'admin_grant', 'admin_deduct', 'refund', 'promo', 'referral', 'expiry');--> statement-breakpoint
 CREATE TYPE "public"."status" AS ENUM('active', 'canceled', 'incomplete', 'incomplete_expired', 'past_due', 'paused', 'trialing', 'unpaid');--> statement-breakpoint
 CREATE TYPE "public"."plan" AS ENUM('free', 'premium', 'enterprise');--> statement-breakpoint

packages/db/migrations/meta/0000_snapshot.json

@@ -1,5 +1,5 @@
 {
-  "id": "f8d7bddc-1efc-4f4a-8ebb-e8278508656e",
+  "id": "a1b0192f-d300-48eb-8f1d-e76c65b030dc",
   "prevId": "00000000-0000-0000-0000-000000000000",
   "version": "7",
   "dialect": "postgresql",
@@ -2792,7 +2792,10 @@
     }
   },
   "schemas": {
-    "pdf": "pdf"
+    "chat": "chat",
+    "pdf": "pdf",
+    "image": "image",
+    "mesh": "mesh"
   },
   "sequences": {},
   "roles": {},

packages/db/migrations/meta/_journal.json

@@ -5,8 +5,8 @@
     {
       "idx": 0,
       "version": "7",
-      "when": 1775335397081,
-      "tag": "0000_sloppy_stryfe",
+      "when": 1775336269295,
+      "tag": "0000_living_namora",
       "breakpoints": true
     }
   ]