Handle missing browser when opening nearby links

[Pygmalion69]

Motivation

• Prevent crashes in NearbyFragment.onItemClick() when startActivity() throws ActivityNotFoundException for external (e.g. Wikipedia) links.
• Do not add a <queries> manifest entry because package-visibility declarations do not install an intent handler and would not prevent startActivity() from throwing.

Description

• Import ActivityNotFoundException and Toast and wrap startActivity(browserIntent) with a try/catch in NearbyFragment.onItemClick().
• On ActivityNotFoundException, display the existing R.string.no_browser_found toast instead of crashing.
• No manifest or other files were modified.

Testing

• Ran git diff --check and git diff --cached --check, both passed.
• Attempted ./gradlew compileFossDebugKotlin, but the build could not run in this environment due to a missing Android SDK location (local.properties/ANDROID_HOME).
• No unit or instrumentation tests were executed in this environment.

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Codex Task