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__/viewer_integration.test.mjs

@@ -62,7 +62,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   // 'native' mode sets HLS = undefined so viewer.js takes the Safari native path.
   const hlsCalls = { instances: [], loaded: false };
   if (hlsMode === 'mocked') {
-    win.HLS = class MockHLS {
+    win.Hls = class MockHLS {
       constructor(opts) {
         hlsCalls.instances.push({ opts, destroyed: false, events: {}, source: null, media: null });
       }
@@ -103,7 +103,7 @@ function createBrowserEnv({ storageData = {}, url = 'https://example.com/viewer/
   } else if (hlsMode === 'native') {
     // Simulate Safari — window.HLS exists but isSupported() returns false.
     // viewer.js then falls through to video.src = manifestUrl (native HLS).
-    win.HLS = class MockHLS_Native {
+    win.Hls = class MockHLS_Native {
       static isSupported() {
         return false; // Safari has native HLS, Hls.js is not needed
       }
@@ -178,15 +178,6 @@ describe('Integration: viewer.js with HLS entries', () => {
             return;
           }
 
-          // HLS detection in console logs
-          const hlsLogs = consoleLogs.filter(
-            (l) => l.includes('HLS detected') || l.includes('HLS')
-          );
-          if (hlsLogs.length === 0) {
-            reject(new Error(`No HLS detection in logs. Logs: ${consoleLogs.join(' | ')}`));
-            return;
-          }
-
           // Verify Hls.js was actually instantiated for the HLS entry
           if (hlsCalls.instances.length < 1) {
             reject(new Error('Expected at least 1 HLS instance, got 0'));
@@ -391,15 +382,6 @@ describe('Integration: viewer.js with HLS entries', () => {
             return;
           }
 
-          // HLS detection in logs
-          const hlsLogs = consoleLogs.filter(
-            (l) => l.includes('HLS detected') || l.includes('HLS')
-          );
-          if (hlsLogs.length === 0) {
-            reject(new Error(`No HLS logs. All: ${consoleLogs.join(' | ')}`));
-            return;
-          }
-
           // Only one HLS instance (for the HLS entry)
           if (hlsCalls.instances.length !== 1) {
             reject(new Error(`Expected 1 HLS instance, got ${hlsCalls.instances.length}`));