fix: restore Instagram media extraction for posts, reels, and stories

[pzzzy]

Summary

This PR restores instantgram support for current Instagram web behavior across posts, reels, and stories.

What changed

• rewrote media selection to target the active visible item instead of the first matching DOM node
• added a shared bookmarklet.js source and bookmarklet-loader.js so all published bookmarklet links stay in sync
• added permalink and page-content fallback resolution for posts, reels, and stories
• fixed Safari video failures by stripping Instagram CDN byte-range params like bytestart and byteend
• stopped forcing modern video URLs onto the legacy generic CDN hostname

User-facing fixes

• photos now open from the item currently in view
• videos now resolve correctly for posts, reels, and stories
• stories no longer default to the first visible item when another one is active
• Safari can open the resolved video URL instead of landing on an invalid CDN fragment

Verification

• verified the new bookmarklet logic against current Instagram web behavior
• confirmed Safari video URLs worked after removing byte-range query params
• ran node --check on:
  • bookmarklet.js
  • bookmarklet-loader.js

Notes

This keeps the published site lightweight while moving the bookmarklet payload into a readable source file, which should make future Instagram compatibility fixes easier to maintain.