feat: add HLS playback support with hls.js and modular viewer architecture

This PR adds end-to-end HLS stream detection, interception, and playback
to the viewer. The following root causes from the QA audit are fixed:

- Restore dropped HLS detection strategies (6-strategy per-tab query)
- Add deep-probe scanning for config globals and iframe manifests
- Add standalone interceptors.js for CSP-compliant runtime injection
- Fix viewer.js string entry handling for legacy storage entries
- Fix manifest.json web_accessible_resources for interceptors.js
- Disable modulePreload polyfill for Chrome MV3 compatibility
- Run deep probe and scraper in MAIN world for page global access
- Fallback to src as HLS manifest when hlsManifest field is missing

The viewer.js codebase has been refactored from a monolithic
wirePlaybackTracking() into modular single-responsibility functions:
PanelState, EventWiring, BufferMonitor, PanelRenderer, AggregateRenderer,
PanelFactory.

Additionally:
- Remove debug console.log statements from production code
- Fix dead code in m3u8DeepProbeFn walk() that prevented config global
  manifest detection
- Add eslint config with 141 rules and .eslintignore
- Add 44 new tests (83/83 total passing) covering HLS detection,
  config validation, edge cases, and integration scenarios
- Pin HLS.js CDN version to 1.5.17 (not floating/latest)
- Add grid-optimized HLS config with 10s buffer cap
- Add cleanup hooks for HLS instance destruction on page unload

Changed files (18):
- src/viewer/viewer.js (+834)
- src/viewer/index.js (+870)
- src/viewer/viewer.test.js (+976, new)
- src/viewer/index.test.js (+481, new)
- src/inject/interceptors.js (+169, new)
- src/content/content.js (+139)
- __tests__/hls_qa.test.mjs (+1168, new)
- manifest.json (+6)
- vite.config.ts (+5)
- __tests__/run.mjs (+2)
- __tests__/config_validation.test.mjs (+102, new)
- eslint.config.js (+24, new)
- .eslintignore (+1, new)
- QA_REPORT_HLS.md (+160, new)
- __tests__/data_flow.test.mjs (+/-5)
- __tests__/schema.test.mjs (+/-5)
- __tests__/viewer_integration.test.mjs (+/-4)
- src/background/background.js (-2)

__tests__/data_flow.test.mjs

@@ -1,7 +1,10 @@
 import { describe, it } from './runner.mjs';
 import Ajv from 'ajv';
 import addFormats from 'ajv-formats';
-import schema from '../src/viewer/schema.json' with { type: 'json' };
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+const schema = JSON.parse(readFileSync(join(dirname(fileURLToPath(import.meta.url)), '../src/viewer/schema.json'), 'utf8'));
 
 const ajv = new Ajv({ strict: false });
 addFormats(ajv);