Add community content disclaimers

Add notes clarifying that community extensions, presets, walkthroughs,
and community friends are independently created and maintained by their
respective authors and are not reviewed, nor endorsed, nor supported
by GitHub.

Disclaimers added to:
- README.md: Community Extensions, Community Presets, Community
  Walkthroughs, and Community Friends sections
- extensions/README.md: Community Reference Catalog and Available
  Community Extensions sections
- presets/README.md: Catalog Management section

Author: mnriem

README.md

@@ -160,6 +160,9 @@ Want to see Spec Kit in action? Watch our [video overview](https://www.youtube.c
 
 ## 🧩 Community Extensions
 
+> [!NOTE]
+> Community extensions are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**. The Community Extensions website is also a third-party resource. Review extension source code before installation and use at your own discretion.
+
 🔍 **Browse and search community extensions on the [Community Extensions website](https://speckit-community.github.io/extensions/).**
 
 The following community-contributed extensions are available in [`catalog.community.json`](extensions/catalog.community.json):
@@ -225,6 +228,9 @@ To submit your own extension, see the [Extension Publishing Guide](extensions/EX
 
 ## 🎨 Community Presets
 
+> [!NOTE]
+> Community presets are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**. Review preset source code before installation and use at your own discretion.
+
 The following community-contributed presets customize how Spec Kit behaves — overriding templates, commands, and terminology without changing any tooling. Presets are available in [`catalog.community.json`](presets/catalog.community.json):
 
 | Preset | Purpose | Provides | Requires | URL |
@@ -236,6 +242,9 @@ To build and publish your own preset, see the [Presets Publishing Guide](presets
 
 ## 🚶 Community Walkthroughs
 
+> [!NOTE]
+> Community walkthroughs are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**.
+
 See Spec-Driven Development in action across different scenarios with these community-contributed walkthroughs:
 
 - **[Greenfield .NET CLI tool](https://github.com/mnriem/spec-kit-dotnet-cli-demo)** — Builds a Timezone Utility as a .NET single-binary CLI tool from a blank directory, covering the full spec-kit workflow: constitution, specify, plan, tasks, and multi-pass implement using GitHub Copilot agents.
@@ -254,6 +263,9 @@ See Spec-Driven Development in action across different scenarios with these comm
 
 ## 🛠️ Community Friends
 
+> [!NOTE]
+> Community projects listed here are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**.
+
 Community projects that extend, visualize, or build on Spec Kit:
 
 - **[cc-sdd](https://github.com/rhuss/cc-sdd)** - A Claude Code plugin that adds composable traits on top of Spec Kit with [Superpowers](https://github.com/obra/superpowers)-based quality gates, spec/code review, git worktree isolation, and parallel implementation via agent teams.

extensions/README.md

@@ -24,6 +24,9 @@ specify extension search  # Now uses your organization's catalog instead of the
 
 ### Community Reference Catalog (`catalog.community.json`)
 
+> [!NOTE]
+> Community extensions are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**. Review extension source code before installation and use at your own discretion.
+
 - **Purpose**: Browse available community-contributed extensions
 - **Status**: Active - contains extensions submitted by the community
 - **Location**: `extensions/catalog.community.json`
@@ -68,6 +71,9 @@ specify extension add <extension-name> --from https://github.com/org/spec-kit-ex
 
 ## Available Community Extensions
 
+> [!NOTE]
+> Community extensions are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**. The Community Extensions website is also a third-party resource. Review extension source code before installation and use at your own discretion.
+
 🔍 **Browse and search community extensions on the [Community Extensions website](https://speckit-community.github.io/extensions/).**
 
 See the [Community Extensions](../README.md#-community-extensions) section in the main README for the full list of available community-contributed extensions.

presets/README.md

@@ -67,6 +67,9 @@ Presets **override**, they don't merge. If two presets both provide `spec-templa
 
 Presets are discovered through catalogs. By default, Spec Kit uses the official and community catalogs:
 
+> [!NOTE]
+> Community presets are independently created and maintained by their respective authors. They are **not reviewed, nor endorsed, nor supported by GitHub**. Review preset source code before installation and use at your own discretion.
+
 ```bash
 # List active catalogs
 specify preset catalog list