feat: add demo database seeding for end-to-end exploration

Add a comprehensive demo seeding system that gives new users a ready-to-explore
e-commerce database with:

- demo_shop database: 100 products, 500 customers, 5000+ orders with realistic
  data patterns including intentionally suboptimal queries for recommendations
- Pre-configured index recommendations and slow query analysis
- Sample saved queries in the SQL Editor (revenue reports, analytics, examples)
- Sample agent conversation history
- Scoped demo users (analyst, developer, viewer)

Usage:
  - Manual: ./scripts/self-host/seed-demo-data.sh
  - Auto during install: DEEPSQL_SEED_DEMO_DATA=1 ./scripts/self-host/install.sh

Files added:
  - docker/postgres/init/10_create_demo_shop.sql: E-commerce schema + sample data
  - scripts/self-host/seed-demo-data.sh: Orchestration script for full seeding

Files modified:
  - scripts/self-host/install.sh: Optional demo seeding integration
  - .env.example: Document new DEEPSQL_SEED_* environment variables
  - README.md: Document demo database and seed-demo-data.sh script

Co-authored-by: Venkat SF <venkatesh.sakamuri@stayflexi.com>

Author: cursoragent

.env.example

@@ -136,6 +136,15 @@ EMBEDDING_FAIL_OPEN=false
 #DEEPSQL_SKIP_AGENT_SETUP=0
 #DEEPSQL_SMOKE_AGENT=1
 
+# ── Demo Data Seeding ───────────────────────────────────────────────────────
+# Seed a ready-to-explore demo database with sample e-commerce data, users,
+# saved queries, slow query history, and index recommendations.
+# Set to 1 to automatically run seed-demo-data.sh during install.
+# Can also be run manually: ./scripts/self-host/seed-demo-data.sh
+#DEEPSQL_SEED_DEMO_DATA=0
+#DEEPSQL_SEED_CONNECTION_NAME=Demo Shop (E-commerce)
+#DEEPSQL_SEED_SKIP_DEMO_DB=0
+
 # ── The /api/llm/v1 agent gateway ───────────────────────────────────────────
 # The DeepSQL CLI agent (`@deepsql/mcp`) points its model at <backend>/api/llm/v1
 # and authenticates with a DeepSQL token; the backend forwards those calls

README.md

@@ -249,10 +249,28 @@ your schema — all from one shared brain.
 ```bash
 ./scripts/self-host/status.sh                    # compose ps + health probes
 ./scripts/self-host/smoke-test.sh                # end-to-end check against the vault DB
+./scripts/self-host/seed-demo-data.sh            # seed demo e-commerce database for exploration
 ./scripts/self-host/uninstall.sh                 # stop and remove containers, keep data
 ./scripts/self-host/uninstall.sh --purge-data    # also drop the volumes
 ```
 
+### Demo Database
+
+To explore DeepSQL features without connecting your own database, run:
+
+```bash
+./scripts/self-host/seed-demo-data.sh
+```
+
+This creates a **demo_shop** e-commerce database with:
+- 100 products, 500 customers, 5,000+ orders
+- Intentionally suboptimal query patterns (to trigger recommendations)
+- Pre-configured slow query analysis and index recommendations
+- Sample saved queries in the SQL Editor
+- Sample agent conversation history
+
+Alternatively, set `DEEPSQL_SEED_DEMO_DATA=1` in `.env` before running `install.sh` to seed automatically.
+
 Upgrading:
 
 ```bash