feat: add proxy support for SDK downloads (v1.1.0)

Add --proxy and --no-proxy global flags to control HTTP/HTTPS proxy
usage for all network operations (SDK installs, FTC SDK clone/fetch,
Android SDK download).

Proxy resolution priority:
  1. --no-proxy          → go direct, ignore everything
  2. --proxy <url>       → use the specified proxy
  3. HTTPS_PROXY / HTTP_PROXY env vars (auto-detected)
  4. Nothing             → go direct

Key implementation details:
- reqwest client is always built through ProxyConfig::client() rather
  than Client::new(), so --no-proxy actively suppresses env-var
  auto-detection instead of just being a no-op.
- git2/libgit2 has its own HTTP transport that doesn't use reqwest.
  GitProxyGuard is an RAII guard that temporarily sets/clears the
  HTTPS_PROXY env vars around clone and fetch operations, then restores
  the previous state on drop. This avoids mutating ~/.gitconfig.
- Gradle wrapper reads HTTPS_PROXY natively; no programmatic
  intervention needed.
- All network failure paths now print offline/air-gapped installation
  instructions automatically, covering manual SDK installs and Gradle
  distribution download.

Closes: v1.1.0 proxy support milestone

src/commands/sdk.rs

@@ -1,60 +1,61 @@
 use anyhow::Result;
 use colored::*;
 use crate::sdk::SdkConfig;
+use crate::sdk::proxy::ProxyConfig;
 
-pub fn install_sdks() -> Result<()> {
+pub fn install_sdks(proxy: &ProxyConfig) -> Result<()> {
     println!("{}", "Installing SDKs...".bright_yellow().bold());
     println!();
-    
+
     let config = SdkConfig::new()?;
-    
+
     // Install FTC SDK
-    crate::sdk::ftc::install(&config.ftc_sdk_path, &config.android_sdk_path)?;
-    
+    crate::sdk::ftc::install(&config.ftc_sdk_path, &config.android_sdk_path, proxy)?;
+
     // Install Android SDK
-    crate::sdk::android::install(&config.android_sdk_path)?;
-    
+    crate::sdk::android::install(&config.android_sdk_path, proxy)?;
+
     println!();
     println!("{} All SDKs installed successfully", "✓".green().bold());
     config.print_status();
-    
+
     Ok(())
 }
 
 pub fn show_status() -> Result<()> {
     let config = SdkConfig::new()?;
     config.print_status();
-    
+
     // Verify SDKs
     println!();
     println!("{}", "Verification:".bright_yellow().bold());
-    
+
     match crate::sdk::ftc::verify(&config.ftc_sdk_path) {
         Ok(_) => println!("{} FTC SDK is valid", "✓".green()),
         Err(e) => println!("{} FTC SDK: {}", "✗".red(), e),
     }
-    
+
     match crate::sdk::android::verify(&config.android_sdk_path) {
         Ok(_) => println!("{} Android SDK is valid", "✓".green()),
         Err(e) => println!("{} Android SDK: {}", "✗".red(), e),
     }
-    
+
     println!();
-    
+
     Ok(())
 }
 
-pub fn update_sdks() -> Result<()> {
+pub fn update_sdks(proxy: &ProxyConfig) -> Result<()> {
     println!("{}", "Updating SDKs...".bright_yellow().bold());
     println!();
-    
+
     let config = SdkConfig::new()?;
-    
+
     // Update FTC SDK
-    crate::sdk::ftc::update(&config.ftc_sdk_path)?;
-    
+    crate::sdk::ftc::update(&config.ftc_sdk_path, proxy)?;
+
     println!();
     println!("{} SDKs updated successfully", "✓".green().bold());
-    
+
     Ok(())
-}
+}