fix: sync Help navigation with browser history

[QuickMythril]

Summary

• add a unified route codec for feedback lists, posts, the composer, and Developer Reference
• preserve Home bridge/display parameters and fragments while changing Help-owned route keys
• restore full Help workspace state on browser Back/Forward, including exact-post loading
• use replacement history for post-publication, deletion, and invalid-route canonicalization
• bump the QDN app version to 1.4.8

Validation

• npm test (129 tests)
• npm run build
• git diff --check
• headless Chromium Back/Forward walkthrough against the production preview and live local feedback data