use hook-specific filenames to avoid overwrites

Multiple hooks in the same plugin directory were overwriting each
other's stdout.log, stderr.log, hook.pid, and cmd.sh files. Now
each hook uses filenames prefixed with its hook name:
- on_Snapshot__20_chrome_tab.bg.stdout.log
- on_Snapshot__20_chrome_tab.bg.stderr.log
- on_Snapshot__20_chrome_tab.bg.pid
- on_Snapshot__20_chrome_tab.bg.sh

Updated:
- hooks.py run_hook() to use hook-specific names
- core/models.py cleanup and update_from_output methods
- Plugin scripts to no longer write redundant hook.pid files

archivebox/plugins/redirects/on_Snapshot__31_redirects.bg.js

@@ -19,7 +19,7 @@ const puppeteer = require('puppeteer-core');
 const PLUGIN_NAME = 'redirects';
 const OUTPUT_DIR = '.';
 const OUTPUT_FILE = 'redirects.jsonl';
-const PID_FILE = 'hook.pid';
+// PID file is now written by run_hook() with hook-specific name
 const CHROME_SESSION_DIR = '../chrome';
 
 // Global state
@@ -274,8 +274,8 @@ async function main() {
         // Set up redirect listener BEFORE navigation
         await setupRedirectListener();
 
-        // Write PID file
-        fs.writeFileSync(path.join(OUTPUT_DIR, PID_FILE), String(process.pid));
+        // Note: PID file is written by run_hook() with hook-specific name
+        // Snapshot.cleanup() kills all *.pid processes when done
 
         // Wait for chrome_navigate to complete (BLOCKING)
         await waitForNavigation();