fix(web,server): improve runtime error visibility in thread error banner

[ecatuogno1]

Summary

• Increase server-side runtime error truncation limit from 180 to 512 characters to preserve diagnostic detail
• Expand UI error banner from line-clamp-3 to line-clamp-6 so longer error messages remain readable without dominating the viewport

Problem

Runtime errors (e.g. malformed local SKILL.md with invalid YAML frontmatter) are truncated twice: server-side to 180 chars, then UI-side to 3 lines via line-clamp-3. This makes errors like invalid YAML parsing failures nearly unreadable — the user has to take a screenshot fast before the banner disappears, and even then the text is cut off.

Test plan

• Trigger a runtime error with a long message (e.g. malformed .agent/skills/.../SKILL.md)
• Verify the error banner shows enough text to diagnose the issue (up to 6 lines)
• Verify short errors still render cleanly without excess whitespace
• Server tests pass (bun run test in apps/server)

Closes #1084

Note

Improve runtime error visibility in thread error banner

• Expands the error description in ThreadErrorBanner from 3 to 6 visible lines before clamping.
• Passes an explicit 512 character limit to truncateDetail for runtime.error activity messages in ProviderRuntimeIngestion.ts, replacing the previous default truncation length.

^{Macroscope summarized 86b53ae.}

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[binbandit]

Is there a chance we can get an example image attached?

[ecatuogno1]

@binbandit Here’s the repro screenshot from #1084 showing the current truncated error banner state that this PR is fixing.

This change keeps the same banner UI, but increases the visible clamp from 3 lines to 6 and preserves up to 512 chars server-side instead of 180, so the same error is much more readable.

[ecatuogno1]

@binbandit Fresh after screenshot from this PR branch.

This is the expanded thread error banner with the same kind of long malformed-SKILL.md runtime error, so you can see the 6-line clamp / higher truncation limit effect directly.