Fix stale pending steer projection

[brsbl]

Summary

• stop projecting unaccepted steers after their target turn completes
• treat pending steers as latest-page tail state so historical pages cannot resurrect stale requests
• add unit, CLI-rendering, and database-backed pagination regressions

Root cause

The timeline treated any unaccepted steer as pending whenever the overall thread remained active. It did not distinguish thread activity from the lifecycle of the steer’s expected target turn. After durable request-settlement state was removed, a completed target with later unrelated active work could leave the old steer visible indefinitely.

Validation

• pnpm exec turbo run test --filter=@bb/thread-view --force — 343 tests passed
• pnpm exec turbo run test --filter=@bb/server --force -- test/services/threads/timeline-parented-pagination.test.ts — 3 tests passed
• pnpm exec turbo run typecheck --filter=@bb/thread-view --force
• pnpm exec turbo run typecheck --filter=@bb/server --force
• staged review loop completed with no remaining P0/P1 findings