feat(Archive ObjC GooglePlacesDemos): API key via Secrets.xcconfig + fix Pods [6/8]

[iHackSubhodip]

What

• Fixes an orphaned CocoaPods setup: adds GooglePlacesDemos to the Archive
  Podfile + a shared GooglePlaces-Objc.xcworkspace so pod install wires it
  (it was Pods-wired in the pbxproj but missing from the Podfile → couldn't build).
• Deletes tracked SDKDemoAPIKey.h; DemoAppDelegate.m reads PLACES_API_KEY from
  the bundle via objectForInfoDictionaryKey:, fail-closed (NSException).
• Adds tracked GooglePlacesDemos.xcconfig wrapper (#include? "Secrets.xcconfig").
• Info.plist maps PLACES_API_KEY → $(PLACES_API_KEY).
• project.pbxproj: wires the wrapper as a project-level base configuration.

Why

• Removes the key from a tracked source file (the old #error + constant pattern);
  unifies onto the shared Secrets.xcconfig mechanism.
• Un-breaks the archived app's build — mirrors the active-app fix in feat(GooglePlacesSwiftDemos): API key via Secrets.xcconfig + fix Pods [4/8] #31.

When

• Series [6/8]; first of the two archived Objective-C apps.

Setup / testing

• cd Archive/GooglePlaces-Objc && pod install; create
  GooglePlacesDemos/Secrets.xcconfig with PLACES_API_KEY = ….
• Build from GooglePlaces-Objc.xcworkspace → launches; remove Secrets → builds, fail-closed.
• plutil -lint on project.pbxproj passes.

Test

Simulator.Screen.Recording.-.iPhone.17.Pro.-.2026-08-07.at.18.57.53.mov