feat: add app_context_changed event type

[zimeg]

Summary

• Adds AppContextChangedEvent to @slack/types with a discriminated union for entity types (slack#/types/channel_id, slack#/types/canvas_id, slack#/types/list_id, slack#/types/message_context)
• Adds app_context optional field to GenericMessageEvent (the context is delivered inline on messages too)
• Makes thread_ts optional on AssistantThreadsSetSuggestedPromptsArguments in @slack/web-api — agent_view DMs set prompts at the channel level without a thread

Test plan

• npm run build --workspace=@slack/types passes
• npm run build --workspace=@slack/web-api passes
• Bolt JS can resolve the event via app.event('app_context_changed', ...) using Extract<SlackEvent, { type: 'app_context_changed' }>
• setSuggestedPrompts accepts calls without thread_ts

🤖 Generated with Claude Code

[changeset-bot]

⚠️ No Changeset found

Latest commit: 3ee37fb

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.90%. Comparing base (fefeb07) to head (3ee37fb).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2633   +/-   ##
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  Coverage   88.90%   88.90%           
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  Files          63       63           
  Lines       10256    10256           
  Branches      452      452           
=======================================
  Hits         9118     9118           
  Misses       1117     1117           
  Partials       21       21           

Flag	Coverage Δ
cli-hooks	88.90% <ø> (ø)
cli-test	88.90% <ø> (ø)
logger	88.90% <ø> (ø)
oauth	88.90% <ø> (ø)
socket-mode	88.90% <ø> (ø)
web-api	88.90% <ø> (ø)
webhook	88.90% <ø> (ø)

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