feat(skills): add interactive captain aside sessions

[Quidge]

Intent

Author a terse, captain-invocable /aside skill at .agents/skills/aside/SKILL.md in the firstmate repo. /aside opens a dedicated interactive window (an interactive scout / human-in-the-loop session) that the captain talks to DIRECTLY for ad-hoc, multi-turn context-gathering, instead of loading everything into the main firstmate chat; on conclusion it hands its outcome back to the main firstmate session.

Deliberate design decisions: (1) The skill builds on fm-spawn.sh's --scout shape, chosen as the lightest viable spawn that fm-spawn cleanly supports for a non-ship, non-secondmate window - scout already yields a scratch worktree plus the report.md + status-line conclusion contract with no PR and no delivery-mode machinery. (2) The aside session is deliberately INTERACTIVE WITH THE CAPTAIN: it explicitly bends hard rule 4 (a crewmate never addresses the captain) for this one opt-in session only, while every other supervision and safety rule still holds - this bend is intentional, not a mistake. (3) The session concludes only when the captain says so, writing its outcome to data//report.md and appending a done: status line so the main firstmate reconciles it and tears the window down. (4) Required frontmatter: name: aside, a description covering what it does and when the captain invokes it, user-invocable: true, metadata.internal: true.

Accepted follow-up requirement folded in during review: the /aside session MUST append 'paused: awaiting captain' to its status file between the captain's turns, so firstmate treats its idle as a bounded human-wait rather than a possible wedge/hang; the skill documents that firstmate reconciles an aside's idle as healthy (a captain conversation in progress) and rechecks on the long paused cadence until done.

Scope is intentionally minimal/terse v1 - capture the essence only (spawn the window, interactive-with-captain, conclude back to main firstmate, teardown), not an over-built control plane; the captain will iterate. This touches firstmate's shared tracked material (.agents/skills/), authored per firstmate-coding-guidelines: one sentence per line in Markdown, plain dashes not em dashes, size discipline, trigger declared via user-invocable frontmatter, no agent commit co-author.

What Changed

• Add the captain-invocable /aside skill for direct, multi-turn conversations in an isolated scout window.
• Define healthy paused: awaiting captain handling and captain-triggered handback through the scout report, status, and teardown contracts.
• Register the skill as an agent-runtime documentation surface.

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ **Rebase** - passed

✅ **Review** - completed

✅ **Test** - passed

✅ **Document** - passed

✅ **Lint** - passed

✅ **Push** - passed