feat: panel refinements - toggles, no WCs, persistence

[auniverseaway]

• Remove Lit-based nx-panel block (panel.js/panel.css) in favor of
  utils/panel.js with plain DOM createPanel/showPanel/hidePanel functions
• Move panel styles from shadow DOM CSS to global styles.css
• Add action-button block to toggle before/after panels via fragments
• Extract api.js with daFetch (auth-aware), ping, source, list, signout
• Rewrite utils.js: environment-aware DA service origins via getEnv,
  improved parseWindowPath (returns null for invalid, strips /index)
• CSS: replace JS-added classes (spectrum-edge, app-frame) with
  meta-content attribute selectors
• Simplify profile color scheme toggle, import signout from api.js
• Add unit tests for utils (parseWindowPath, getEnv, loadStyle) and
  test mocks (IMS, CSS)
• Panel-aware default-content max-width when side panels are visible

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

Panels

https://nx2fixes--da-nx--adobe.aem.page/drafts/cmillar/panels

DA.LIVE prod + this NX2 PR + NX1

https://main--da-live--adobe.aem.live/?nx=nx2fixes
Expectation: this works E2E

DA.LIVE stage + this NX2 PR + NX2

https://dasites--da-live--adobe.aem.page/?nx=nx2fixes&nxver=2
Expectation: only da homepage works, but is correctly styled

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Commits

• f384ff4 ✅ (latest)

[auniverseaway]

@hannessolo I really love the approach to panels. Two things about this PR:

1. I made some small tweaks to the panel implementation...
   1. You can trigger by link (i.e. button)
   2. I think this is a base-level feature, so moved the styles into styles.css.
   3. I moved us away from the web component as it seemed a bit redundant and I'm worried that we'll get into shadow dom query selector hell later down the road.
2. I'm combining this my other relatively foundational PR. I removed the unrelated changes. This is now only the updates required for the panels.

Hopefully this works for you!

[auniverseaway]

Some non-critical open questions / comments:

We could easily ditch the fragments in favor of just loading a block directly. We would lose flexibility in that we could associate different blocks in authoring without a release, but I'm not sure we would actually use this. We may want to slice this differently anyway...

It seems like we pretty much know what we want each panel to always be:

1. left panel - chat
2. right panel - auxilary features (browse, recents, etc.)

I think this is good for now. Later down the road we may want to allow different views to determine what panels they get. This will be especially true if the auxilery panel becomes a nightmare to support.