SRE-715: Add PR-title preflight workflow + bump SHA pins

[TimDiekmann]

Summary

• Wires the new reusable preflight-pr-title.yml workflow into this repo's preflight chain.
• Bumps every hashintel/.github reusable-workflow SHA pin (preflight + housekeeping) to e12e306 in one atomic change — Renovate would have done the bump on its next pass; doing it here keeps the change reviewable as a single PR.

The new check enforces that human-authored PR titles include a Linear issue ID (e.g. H-1234, BE-5678) in the prefix segment. Bot-authored PRs (hash-worker[bot], dependabot[bot], …) are skipped automatically.

Related: SRE-715, follow-up of the source change in hashintel/.github#65 (H-6402 was the original rollout of the preflight chain).

Test plan

• Preflight PR title job runs and passes on this PR (title contains SRE-715)
• Other preflight jobs (stale-approvals, dependencies, todo-comments) still pass after the SHA bump
• Housekeeping workflow continues to function with the new pin

[cursor]

PR Summary

Medium Risk
Moderate risk because it changes CI gating by adding a new PR-title validation job and updates pinned SHAs for reusable workflows, which could unexpectedly fail or alter preflight/housekeeping behavior.

Overview
Adds a new preflight job (pr-title) via the shared hashintel/.github reusable workflow to enforce PR title conventions.

Updates the pinned hashintel/.github reusable-workflow SHAs across preflight.yml and housekeeping.yml from a0df113... to e12e306... to pick up the latest shared workflow behavior.

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[augmentcode]

🤖 Augment PR Summary

Summary: Adds a preflight PR-title check to enforce Linear issue IDs in human-authored PR titles.

Changes: Wires in preflight-pr-title.yml and bumps all hashintel/.github reusable-workflow pins (preflight + housekeeping) to e12e306.

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[augmentcode]

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