docs: sonos-s2-setup - Content Actions must be configured for rating icons to appear

[schmitzkr]

Closes #315

The setup guide currently says to leave Content Actions as "No changes" (line 125-126). This means the rating/heart icon never appears anywhere in the Sonos app, for any track, regardless of bonob's rateItem implementation.

Per Sonos's current docs (docs.sonos.com/docs/configure-ratings, develop-ratings), rating icons on the Now Playing screen are driven entirely by a manually configured Content Actions entry on the Integration Submission Form, separate from the dynamic/PresentationMap mechanism bonob implements itself. That implementation is correct and necessary but not sufficient on its own in the current app.

This PR replaces "No changes" with the working config for a simple love/heart toggle, matching bonob's own ratingAsInt encoding in src/smapi.ts (unrated = 100, loved = 101):

• Content Action: resources Track, placement NOW_PLAYING
• State 100 (unrated): icon HEART_UNSELECTED, On Action Set Value 101
• State 101 (loved): icon HEART_SELECTED, On Action Set Value 100
• Each state's On Action Set Value must point at the other state, not itself, or the button becomes an inert no-op
• Also notes the separate Service Configuration Refresh then Send step needed to actually deploy the change, plus the app restart needed to pick it up

Confirmed working end to end on v0.12.0 against a Navidrome backend, Sonos S2, Android app.