Add Truth Bear (GAUGE) integration

integrations/truthbear.md

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+---
+layout: integration
+name: Truth Bear (GAUGE)
+description: Verify official facts with Bitcoin-anchored proof for Haystack pipelines.
+authors:
+  - name: changchinfu
+    socials:
+      github: CHANGCHINFU
+pypi: https://pypi.org/project/mcp-gauge-x402
+repo: https://github.com/CHANGCHINFU/mcp-gauge
+type: Data Ingestion
+report_issue: https://github.com/CHANGCHINFU/mcp-gauge/issues
+logo: /logos/truthbear.png
+version: Haystack 2.0
+toc: true
+---
+
+### Table of Contents
+
+- [Overview](#overview)
+- [Usage](#usage)
+- [License](#license)
+
+## Overview
+
+[Truth Bear (GAUGE)](https://truthbear.co) returns verifiable official-source records for AI pipelines.
+Every record carries:
+
+- The **official source URL** (FRED, USGS, SEC EDGAR, NOAA, EPA, and 180+ signals)
+- A **SHA-256 record_hash** anchored to Bitcoin via daily Merkle tree + OpenTimestamps
+- A **freshness stamp** and Ed25519 signature
+
+Bundle tiers cross-check 3 independent official sources against each other.
+
+Screening-level factual grounding, not decision-grade advice. If the data cannot be found, you do not pay.
+
+## Usage
+
+Truth Bear is available as an MCP server ([mcp-gauge-x402](https://www.npmjs.com/package/mcp-gauge-x402))
+and via REST API at `https://api.truthbear.co`.
+
+### REST API in a Haystack pipeline
+
+```python
+import requests
+from haystack import Document
+
+def get_verified_fact(query: str) -> Document:
+    resp = requests.get(
+        "https://api.truthbear.co/trust/preview",
+        params={"q": query}
+    )
+    data = resp.json()
+    return Document(
+        content=f"{data.get('value', '')} (source: {data.get('source_url', '')})",
+        meta={
+            "record_hash": data.get("record_hash"),
+            "source_url": data.get("source_url"),
+            "freshness": data.get("freshness"),
+        }
+    )
+
+fact = get_verified_fact("US unemployment rate")
+print(fact.content)
+print(f"record_hash: {fact.meta['record_hash']}")
+```
+
+### MCP Server
+
+Install and run the MCP server for full x402-paid access:
+
+```bash
+npx mcp-gauge-x402
+```
+
+Free tools (catalog, preview, sample, anchor verification) require no wallet.
+Paid tools settle per call via x402 (USDC on Base) with no API key or signup.
+
+### Key features
+
+- **180+ signals** from official government sources
+- **Bitcoin-anchored proof**: every record hash is independently re-verifiable
+- **3-source cross-validation** in bundle tiers
+- **No prediction, no advice**: descriptive only
+
+## License
+
+MIT