fix: slack section limiting

[themarolt]

Note

Low Risk
Low risk: changes only Slack notification block construction to avoid per-section length errors, though it could slightly alter message formatting/truncation for very long lines.

Overview
Fixes Slack Block Kit section length violations by introducing splitIntoSectionBlocks, which splits long message text into multiple section blocks at newline boundaries and hard-truncates any single line that exceeds the per-section character limit.

buildContentBlocks now uses this splitter for both plain-string content and titled SlackMessageSection content, reducing the chance of Slack rejecting oversized section blocks.

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[Copilot]

Pull request overview

Adjusts Slack notification formatting to better respect Slack’s per-section text limits by splitting long section content into multiple blocks.

Changes:

• Introduces a conservative MAX_SECTION_TEXT limit for Slack section blocks.
• Updates buildContentBlocks to split oversized section text at newline boundaries into multiple section blocks.
• Simplifies the single-string content path to return a single section block.

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[github-actions]

⚠️ Jira Issue Key Missing

Your PR title doesn't contain a Jira issue key. Consider adding it for better traceability.

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• feat: add user authentication (CM-123)
• feat: add user authentication (IN-123)

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• CM: Community Data Platform
• IN: Insights

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