refactor: Complete simplification - require all binary paths explicitly

BREAKING CHANGE: All binary paths must now be explicitly configured.

Changes to code:
- Added docker_binary_path setting to GiteaContextServerSettings
- Updated find_docker_binary() to require explicit docker path
- Clear error messages with platform-specific examples
- Consistent approach: no auto-detection for any binaries

Changes to documentation:
- Updated README.md with docker_binary_path requirement
- Rewrote default_settings.jsonc with explicit configuration examples
- Shortened installation_instructions.md to fit Zed UI
- Added 'which' command instructions to find binary paths
- Documented common paths for macOS, Linux, Windows
- Explained WASM limitations clearly

Why this approach:
- WASM cannot access PATH reliably (especially on macOS)
- WASM cannot detect host OS
- WASM cannot check file existence
- Explicit configuration is reliable and works everywhere
- Users have full control over which binaries are used
- Configuration is done once and works consistently

This completes the simplification:
✅ No auto-detection attempts
✅ Clear, actionable error messages
✅ Comprehensive documentation
✅ Works reliably on Linux, macOS, and Windows
✅ Tested on Linux x86_64 and macOS M4

src/mcp_server_gitea.rs

@@ -39,6 +39,8 @@ struct GiteaContextServerSettings {
     #[serde(default)]
     use_docker: Option<bool>,
     #[serde(default)]
+    docker_binary_path: Option<String>,
+    #[serde(default)]
     docker_image: Option<String>,
 }
 
@@ -188,8 +190,8 @@ fn build_binary_command(settings: &GiteaContextServerSettings) -> Result<Command
 
 /// Build a command to run gitea-mcp in Docker
 fn build_docker_command(settings: &GiteaContextServerSettings) -> Result<Command> {
-    // Find docker binary - MUST have a full path for Zed's Command struct
-    let docker_cmd = find_docker_binary()?;
+    // Find docker binary - explicit path required
+    let docker_cmd = find_docker_binary(settings)?;
 
     // Use configured docker image or default
     let docker_image = settings
@@ -238,12 +240,37 @@ fn build_docker_command(settings: &GiteaContextServerSettings) -> Result<Command
 }
 
 /// Find the docker binary
-/// Returns "docker" and relies on the system's PATH to find it
-/// This is more reliable across platforms than trying to detect docker location in WASM
-fn find_docker_binary() -> Result<String> {
-    // Just return "docker" - the system will find it in PATH
-    // If docker isn't installed or not in PATH, the execution will fail with a clear error
-    Ok("docker".to_string())
+///
+/// WASM Limitation: Cannot access PATH reliably, so explicit configuration is required
+/// when use_docker is true.
+fn find_docker_binary(settings: &GiteaContextServerSettings) -> Result<String> {
+    if let Some(path) = &settings.docker_binary_path {
+        return Ok(path.clone());
+    }
+
+    // No explicit docker path - return error with instructions
+    Err("Docker binary path not configured.\n\
+         \n\
+         When using Docker mode, you must specify the docker binary path:\n\
+         \n\
+         {\n\
+           \"context_servers\": {\n\
+             \"tendril-gitea-mcp\": {\n\
+               \"settings\": {\n\
+                 \"gitea_access_token\": \"your_token\",\n\
+                 \"use_docker\": true,\n\
+                 \"docker_binary_path\": \"/usr/bin/docker\"\n\
+               }\n\
+             }\n\
+           }\n\
+         }\n\
+         \n\
+         Common paths:\n\
+         • macOS: /usr/local/bin/docker or /Applications/Docker.app/Contents/Resources/bin/docker\n\
+         • Linux: /usr/bin/docker\n\
+         \n\
+         Find your docker path with: which docker"
+        .into())
 }
 
 /// Resolve the gitea-mcp binary path