fix: remove duplicate h1 headers from docs index pages

The docs framework (fumadocs) renders the frontmatter `title` as an h1.
Having a matching `# Title` in the content creates duplicate h1 tags on
the page. Removed the content-level h1 from tools, concepts, contributing,
and examples index pages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

apps/docs/content/docs/concepts/index.mdx

@@ -3,8 +3,6 @@ title: Core Concepts
 description: Understand the building blocks of GitMem's institutional memory system.
 ---
 
-# Core Concepts
-
 GitMem is built around a few key ideas that work together to give AI agents persistent, actionable memory.
 
 ## The Memory Loop

apps/docs/content/docs/contributing/index.mdx

@@ -3,8 +3,6 @@ title: Contributing
 description: How to contribute to GitMem.
 ---
 
-# Contributing
-
 GitMem is open source. Contributions are welcome.
 
 ## Development Setup

apps/docs/content/docs/examples/index.mdx

@@ -3,8 +3,6 @@ title: Examples
 description: Real stories of institutional memory preventing mistakes.
 ---
 
-# Examples
-
 These are real stories from production AI agent workflows — anonymized, but not invented. Each one follows the same arc:
 
 1. **The Situation** — An agent hits a problem during real work

apps/docs/content/docs/tools/index.mdx

@@ -3,8 +3,6 @@ title: Tool Reference
 description: Complete reference for all GitMem MCP tools.
 ---
 
-# Tool Reference
-
 GitMem exposes tools via the [Model Context Protocol](https://modelcontextprotocol.io). Each tool has a canonical name and short aliases for convenience.
 
 ## Core Tools (All Tiers)