Add shared materialization policy to chat and collaboration adapters

[khaliqgant]

Context

Tracking issue for applying the shared materialization policy from #194 to chat/collaboration adapters where channel/message history sync is expensive.

Umbrella: #195

Candidate adapters

• Slack
• Teams

These should only expose materialization config if the adapter has a bulk/history sync path where lazy channel/team defaults avoid substantial work.

Suggested provider shapes

• Slack: targets such as workspaces/channels, resources such as messages/replies/reactions/users depending on current sync support.
• Teams: targets such as teams/channels/chats, resources such as messages/replies/members depending on current sync support.

Exact names should follow existing canonical paths and adapter config vocabulary.

Acceptance criteria

• Use adapter-core shared materialization utilities.
• Preserve existing eager/default behavior.
• Add provider-specific webhook lazy opt-out names if needed, e.g. webhookWritesForLazyChannels.
• Avoid applying issue-style filters if provider APIs do not support them; define provider-appropriate filters such as since, channel type, archived state, or membership when available.
• Tests cover channel/team exact and glob matching, lazy default, eager selected channel/team, incremental history cursor, and webhook behavior.
• README documents what is and is not materialized lazily.