Add log-future-addition skill for filing a single idea as one issue

[bracyw]

Changes

Adds the log-future-addition skill — a lightweight counterpart to to-prd that files one out-of-scope idea as a single needs-triage issue. It takes the idea from a command arg, else the conversation, else a short prompt; drafts a minimal What/Why body; runs one non-blocking duplicate search; and files only after two-stage consent (offers before running unless explicitly invoked, then confirms the draft before posting). No new label — an idea goes straight into the existing needs-triage queue (plus an obvious type or area when clear), and /triage classifies it like any other intake.

Also pins the Idea term in the glossary, adds a one-line carve-out in issue-tracker.md noting the skill applies needs-triage at creation, and points CLAUDE.md at the skill so an out-of-scope idea gets offered a home instead of being lost.

Notes

• Reuses the existing needs-triage label. An earlier draft added a dedicated idea label, but it was dropped as redundant — a filed idea simply needs triage, which needs-triage already means.
• The skill applies needs-triage at creation, the one documented exception to "triage roles are applied by /triage, not at creation" — consistent with triage's own unlabeled-to-needs-triage intake.
• No ticket exists for this work, so commits are not #NNN-tagged and the Closes line is omitted. Wire in a ticket if one should track it.

Test Cases

• Skill loads and is discoverable by the harness under the expected trigger (out-of-scope idea surfaces mid-work).
• Glossary, issue-tracker, and CLAUDE.md cross-references resolve to the new skill.

Checklist

• All commits are tagged with the ticket number
• No linting errors / newline at end of file warnings
• All code follows repository-configured prettier formatting
• No merge conflicts
• All checks passing
• Remove any non-applicable sections of this template
• Assign the PR to yourself
• No package-lock.json changes (unless dependencies have changed)
• Request reviewers & ping on Slack
• PR is linked to the ticket (fill in the closes line below)