[Improve] Include Linear issue metadata in Memory

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Include Linear issue cycle, estimate, start date, parent, and bounded direct/inverse relationships in an optional ## Metadata section on Memory pages.
• Sort labels, relationship groups, and related issues for stable output, link related issues to their Memory pages, and disclose truncated relationship lists.
• Keep existing status, priority, assignee, creator, team, project, labels, and lifecycle dates in frontmatter without duplicating them in the new section.
• Bump the Linear issue collector version so previously ingested pages replay with the enriched metadata.
• Cover API normalization, populated rendering, absent metadata, and duplicate-field avoidance, and update the Linear integration guide.

Why this change was made

Linear issues expose useful planning and dependency context that the collector did not retain. Memory pages now preserve that context while staying concise and deterministic.

Impact

Agents recalling Linear issues can see cycle, estimation, hierarchy, start timing, and dependency relationships without opening Linear. The collector version bump replays existing history so pages receive the enrichment without waiting for later issue edits; pages with none of those fields remain unchanged apart from deterministic label ordering, and their existing frontmatter metadata stays intact.

[roomote-community]

No code issues found. See task

• Bump the Linear issue collector version so existing Brain pages are replayed with metadata.

_{Reviewed a263fe2}

[roomote-roomote]

Fixed in a263fe21: bumped the Linear issue collector to entity-census-v2 and updated all exact collector-ID assertions, so existing issue pages replay with the new metadata. Focused Types and SDK tests, package typechecks, formatting, oxlint, and pre-push checks pass.