feat(hooks): add block-image-read hook to prevent context overflow

Add PreToolUse hook that intercepts Read tool calls on image files
(.png, .jpg, .webp, etc.) and blocks them with helpful message.

This prevents context exhaustion when image generation skills
produce multiple files and the agent tries to read them (each
image can consume 100K+ tokens).

Configuration:
- Enable via config.yaml: hooks.block_image_read.enabled: true
- Or env var: CCS_BLOCK_IMAGE_READ=1

Hook integration:
- lib/hooks/block-image-read.cjs - the hook script
- src/utils/hooks/image-read-block-hook-env.ts - config loader
- Integrated into all spawn locations (ccs.ts, shell-executor,
  cliproxy-executor)

Closes #426

src/utils/shell-executor.ts

@@ -7,6 +7,7 @@
 import { spawn, ChildProcess } from 'child_process';
 import { ErrorManager } from './error-manager';
 import { getWebSearchHookEnv } from './websearch-manager';
+import { getImageReadBlockHookEnv } from './hooks/image-read-block-hook-env';
 
 /**
  * Escape arguments for shell execution (Windows compatibility)
@@ -28,11 +29,12 @@ export function execClaude(
 
   // Get WebSearch hook config env vars
   const webSearchEnv = getWebSearchHookEnv();
+  const imageReadBlockEnv = getImageReadBlockHookEnv();
 
   // Prepare environment (merge with process.env if envVars provided)
   const env = envVars
-    ? { ...process.env, ...envVars, ...webSearchEnv }
-    : { ...process.env, ...webSearchEnv };
+    ? { ...process.env, ...envVars, ...webSearchEnv, ...imageReadBlockEnv }
+    : { ...process.env, ...webSearchEnv, ...imageReadBlockEnv };
 
   let child: ChildProcess;
   if (needsShell) {