skills: harvest 4 MIT dev skills from obra/superpowers (awesome-claude-skills)

From the ComposioHQ/awesome-claude-skills list. Checked licenses BEFORE copying:
- threat-hunting-with-sigma-rules: repo is gone (GitHub 404) -- not harvested.
- forensics (mhattingpete): repo restructured, those skills no longer exist -- not harvested.
- pdf / mcp-builder (Anthropic official): LICENSE.txt FORBIDS copying out of the
  Service / derivatives / redistribution -- NOT harvestable into this repo (install via
  the official Claude Code marketplace instead if wanted).
- obra/superpowers: MIT -> the only legally harvestable set; imported with attribution.

Imported (each with its own MIT LICENSE copy + SOURCE.md provenance, commit a21956e48c13,
ASCII-normalized to house style, no emojis):
- using-git-worktrees
- test-driven-development (+ testing-anti-patterns.md)
- root-cause-tracing (+ find-polluter.sh helper, emojis -> ASCII markers)
- brainstorming (methodology only; upstream visual websocket server intentionally omitted)

Faithful imports -- content not reworded beyond ASCII typography/emoji normalization.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/brainstorming/SOURCE.md

@@ -0,0 +1,20 @@
+# Source / Provenance
+
+Harvested from obra/superpowers (MIT, Copyright (c) 2025 Jesse Vincent) at commit a21956e48c13 on 2026-06-17.
+
+## Source path
+- `skills/brainstorming/SKILL.md` -> `SKILL.md` (METHODOLOGY ONLY)
+
+## Adaptations (ClaudeTools house style)
+- ASCII typography normalization: 21 non-ASCII characters replaced (em-dash `-` -> `-`; unicode arrow `->` -> `->`).
+- No emojis were present in the source.
+- Added a `NOTE (ClaudeTools)` block near the top recording that the optional visual brainstorming server was intentionally omitted and that this is imported as a methodology reference.
+- No content was otherwise reworded; the brainstorming methodology is preserved as in the source apart from the normalization and the added note.
+
+## Omitted upstream tooling (intentional)
+The optional visual brainstorming companion/server was NOT imported. Specifically, none of the following were fetched or included:
+- `skills/brainstorming/scripts/` (websocket server)
+- `skills/brainstorming/frame-template.html`
+- `skills/brainstorming/visual-companion.md`
+
+The SKILL.md text still references the visual companion (browser server, `--open`, `visual-companion.md`); those references describe upstream tooling that is not present in this import. The added NOTE block flags this for the reader.