Phase 1: ADR-A — new LARQL runner type

[ttupper92618]

Parent: #173
Phase: 1 — Decisions + publisher smoke tier
Depends on: none
Blocks: #157, #159, #163

Goal

Document the integration shape for LARQL as a first-class Skulk runner type.

Decision

Add LarqlRunner as a Worker-managed runner subtype that supervises a child larql-server binary alongside the existing MLX runner path.

Rejected alternatives to capture:

• Sidecar: leaks process lifecycle responsibility outside Skulk and forks operator UX.
• In-tree port: too much work and detaches Skulk from upstream LARQL improvements.

Acceptance criteria

• ADR lands under docs/adr/ with status, context, decision, consequences, and rejected alternatives.
• ADR explicitly states that LarqlRunner lifecycle events flow through Skulk's event-sourcing and runner-status machinery.
• ADR links parent roadmap LARQL slice placement roadmap #173, LARQL upstream, and the source slice-placement plan.
• Architecture docs are updated if the ADR introduces durable architecture terminology.

Validation

• Documentation build or focused docs validation passes.
• No runtime code changes are included in this ADR-only issue.

[ttupper92618]

Implemented in PR #174: #174

This records the Phase 1 decision to add a Worker-managed LarqlRunner that supervises an out-of-process larql-server, instead of embedding LARQL into the existing MLX runner or running it as a detached sidecar.