[Bug]: /speckit-taskstoissues dedup matches bare task IDs across features — valid tasks are silently skipped

## Version

spec-kit v1.0.1 (`.claude/skills/speckit-taskstoissues/SKILL.md`, dedup step around the `list_issues` flow)

## Description

Task IDs like `T001` are local to one feature's `tasks.md` and restart from T001 in every feature. The dedup step, however, matches repository issues by task ID without scoping to the current feature: if feature `001-auth` already produced an issue titled with `T001`, then running `/speckit-taskstoissues` for feature `002-billing` sees "T001 exists" and **skips creating the issue for billing's T001** — a silent gap in the tracker, in exactly the multi-feature repos this command targets.

This is the inverse of #2968 (which was about creating duplicates): the fix direction there makes the matching aggressive enough to now suppress valid tasks.

## Expected behavior

- Include a stable feature identifier (the `NNN-name` spec dir) in each created issue's title or a label, and require **both** the feature identity and the task ID to match before skipping.
- Re-check for existing feature+task issues immediately before creation so two concurrent invocations don't race the fetch-then-create sequence.

Open .claude/skills/speckit-taskstoissues/SKILL.md and inspect the dedup step around the list_issues flow. Trace how the current feature directory and task ID are compared, then verify the behavior for T001 in two feature directories. Done means valid tasks from different features are retained and the feature-plus-task check is repeated immediately before creation.

索引モデルが issue の本文から書いたものです。