feat: Integrate Amazon SP-API for product sellability and pricing

- Added `amazon-sp-api` dependency to package.json.
- Enhanced configuration to include SP-API credentials and settings.
- Implemented SP-API client initialization and error handling in sp-api.ts.
- Developed functions to fetch product sellability and pricing data.
- Updated main processing logic in index.ts to incorporate sellability checks before fetching pricing.
- Modified LLM analysis to account for sellability status and reasons.
- Created a new sp-test.ts script for testing SP-API connectivity and sellability.
- Updated types.ts to define SellabilityInfo and extend SpApiData.
- Enhanced result reporting in writer.ts to include sellability information.

README.md

@@ -8,13 +8,14 @@ Amazon product analysis and lead finder agent. Reads product leads from a CSV/XL
 - Redis (local or Docker)
 - [LM Studio](https://lmstudio.ai) running locally with a model loaded
 - Keepa API key ([keepa.com](https://keepa.com))
+- Amazon SP-API private app credentials (LWA + refresh token + IAM)
 
 ## Setup
 
 ```bash
 bun install
 cp .env.example .env
-# Edit .env and set your KEEPA_API_KEY
+# Edit .env and set your KEEPA_API_KEY and SP-API credentials
 ```
 
 ## Usage
@@ -30,6 +31,14 @@ bun run src/index.ts leads.xlsx
 bun run src/index.ts leads.csv --out results.xlsx
 ```
 
+Quick SP-API connectivity test:
+
+```bash
+bun run src/sp-test.ts
+bun run src/sp-test.ts B07SN9BHVV
+bun run src/sp-test.ts --sellability B07SN9BHVV
+```
+
 ## Input file format
 
 Accepts `.csv` or `.xlsx` files. Column names are matched case-insensitively. Required column:
@@ -89,16 +98,27 @@ ASIN, Name, Brand, Category, Unit Cost, Current Price, Avg Price 90d, Sales Rank
 
 ## Environment variables
 
-| Variable        | Default                    | Description                     |
-| --------------- | -------------------------- | ------------------------------- |
-| `KEEPA_API_KEY` | —                          | **Required.** Keepa API key     |
-| `REDIS_URL`     | `redis://localhost:6379`   | Redis connection URL            |
-| `LLM_URL`       | `http://localhost:1234/v1` | LM Studio API base URL          |
-| `LLM_MODEL`     | `default`                  | Model name to pass to LM Studio |
-| `CACHE_TTL`     | `86400`                    | Redis cache TTL in seconds      |
+| Variable                | Default                    | Description                                                             |
+| ----------------------- | -------------------------- | ----------------------------------------------------------------------- |
+| `KEEPA_API_KEY`         | —                          | **Required.** Keepa API key                                             |
+| `SP_API_CLIENT_ID`      | —                          | LWA app client id from Solution Provider Portal                         |
+| `SP_API_CLIENT_SECRET`  | —                          | LWA app client secret from Solution Provider Portal                     |
+| `SP_API_REFRESH_TOKEN`  | —                          | Refresh token from self-authorization                                   |
+| `SP_API_REGION`         | `na`                       | SP-API endpoint region (`na`, `eu`, `fe`; `us` is accepted as `na`)     |
+| `SP_API_MARKETPLACE_ID` | `ATVPDKIKX0DER`            | Marketplace id used for pricing and fee calls (default: US)             |
+| `SP_API_SELLER_ID`      | —                          | Seller ID used for listing restrictions eligibility checks              |
+| `SP_API_USE_SANDBOX`    | `false`                    | Enable SP-API sandbox mode (`true`/`false`)                             |
+| `AWS_ACCESS_KEY_ID`     | —                          | AWS credentials for SigV4 signing (required in most private app setups) |
+| `AWS_SECRET_ACCESS_KEY` | —                          | AWS credentials for SigV4 signing                                       |
+| `AWS_SESSION_TOKEN`     | —                          | Optional session token when using STS credentials                       |
+| `REDIS_URL`             | `redis://localhost:6379`   | Redis connection URL                                                    |
+| `LLM_URL`               | `http://localhost:1234/v1` | LM Studio API base URL                                                  |
+| `LLM_MODEL`             | `default`                  | Model name to pass to LM Studio                                         |
+| `CACHE_TTL`             | `86400`                    | Redis cache TTL in seconds                                              |
 
 ## Notes
 
 - **Keepa rate limiting**: The client reads `tokensLeft` and `refillRate` from each API response and waits automatically when tokens are exhausted. With a Pro subscription (1 token/min), all 100 ASINs in a batch cost 1 token.
 - **Redis is optional**: If Redis is unavailable the tool runs without caching — every run re-fetches from Keepa.
-- **SP-API**: Fee data is currently stubbed with estimates. The `src/sp-api.ts` module has TODO comments marking where real LWA OAuth + fee endpoint calls should go.
+- **SP-API**: `src/sp-api.ts` now uses `amazon-sp-api` to fetch offer pricing and FBA/FBM fee estimates. If SP-API credentials are missing or a call fails, the tool falls back to conservative fee defaults and keeps processing.
+- **Sandbox vs production**: When `SP_API_USE_SANDBOX=true`, production ASIN calls can be denied. Use sandbox-compatible test data or set it to `false` for live marketplace connectivity.