refactor: apply FAR-95 skills review follow-ups

- Remove `playwright-ephemeral/` and `shannon/` entirely per board direction
- Fix `minimax-image-generation/SKILL.md` so YAML frontmatter is at line 1
- Add `minimax-image-generation/scripts/generate.sh` (argparse, error-checked, executable) and document invoking it via `bash scripts/generate.sh ...`
- Deduplicate `minimax-image-generation/CLAUDE.md` against SKILL.md
- `github-app-token`: write token to `$GH_CONFIG_DIR/.gh-token` (preferred) or `$AGENT_HOME/.gh-token` (fallback), fail loudly if neither is set instead of leaking to `mktemp`
- Refresh root `CLAUDE.md` to match actual directory contents and patterns
- Add root `README.md` with human-facing skills index

Co-Authored-By: Paperclip <noreply@paperclip.ing>

README.md

@@ -0,0 +1,31 @@
+# Skills
+
+A collection of Claude Code skills — reusable tools that extend Claude Code's capabilities. Each skill lives in its own top-level directory and ships a `SKILL.md` (the entry point Claude Code reads when invoking the skill) plus any supporting scripts or references.
+
+## Available skills
+
+| Skill | What it does |
+|---|---|
+| [`github-app-token`](./github-app-token) | Generate a short-lived GitHub App installation access token and authenticate the `gh` CLI with it. |
+| [`minimax-image-generation`](./minimax-image-generation) | Generate images from MiniMax's `image-01` model via the `/v1/image_generation` endpoint. |
+
+## Skill layout
+
+```
+<skill-name>/
+├── SKILL.md              # Required. YAML frontmatter (name, description) + usage docs.
+├── CLAUDE.md             # Optional. Maintainer / implementation notes.
+└── scripts/              # Optional. Bash or other implementation scripts.
+```
+
+Scripts use `set -euo pipefail` and a shared `die()` pattern for error handling. Scripts are invoked via `bash scripts/<name>.sh` (not `./scripts/<name>.sh`) so that they work even when the executable bit did not survive deployment.
+
+## No build / test / lint tooling
+
+There is no centralized build, test, or lint system. Each skill is self-contained and pulls in only standard Unix tools as declared in its `SKILL.md`.
+
+## Contributing
+
+- New skills get a new top-level directory with at minimum a `SKILL.md` that starts with YAML frontmatter on line 1.
+- Keep `SKILL.md` focused on decision flow + user-facing usage. Move implementation details, API references, and rarely-needed tables into `CLAUDE.md` or a `references/` subdirectory to keep per-invocation token cost low.
+- Add a row to the table above.