Add repomix skill for repo packing

skills/repomix/SKILL.md

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+---
+name: repomix
+description: Pack a codebase into a single AI-friendly file using the repomix CLI. Use when the user asks to bundle, snapshot, or export a repository (local or remote) for an LLM, count a repo's token size, or generate a compressed code overview.
+metadata:
+  tool: repomix
+  install: npx
+---
+
+## What I do
+
+Run the `repomix` CLI to merge a repository into one structured file with a file summary, directory tree, and per-file contents. Output is safe to feed to LLMs: secretlint strips files matching known credential patterns, and `.gitignore`/`.ignore`/`.repomixignore` are respected automatically.
+
+## When to use me
+
+- "Pack this repo", "bundle the codebase", "make a snapshot for an LLM"
+- Estimating how many tokens a repo costs before sending it somewhere
+- Getting a compressed structural overview of a large codebase
+- Packing a remote GitHub repo without cloning it
+
+## Setup
+
+No install required; `npx` fetches and caches it:
+
+```bash
+npx -y repomix@latest --version   # verify, ~1.18+
+```
+
+## Common invocations
+
+```bash
+# Pack current repo (writes ./repomix-output.xml)
+npx -y repomix
+
+# Pack a specific directory or glob selection
+npx -y repomix path/to/dir
+npx -y repomix --include "src/**/*.ts,*.md" --ignore "**/*.test.ts"
+
+# Output to stdout (pipe or capture) instead of a file
+npx -y repomix --stdout
+
+# Other output formats
+npx -y repomix --style markdown|json|plain -o out.md
+
+# Compressed structural overview (tree-sitter, drops function bodies)
+npx -y repomix --compress
+
+# Remote repo (no clone needed); branch/tag/commit via --remote-branch
+npx -y repomix --remote user/repo
+
+# Token budget guard: non-zero exit if output exceeds N tokens
+npx -y repomix --token-budget 100000
+
+# Show per-file token counts before committing to a full pack
+npx -y repomix --token-count-tree
+```
+
+## Workflow
+
+1. For large repos, run `--token-count-tree` first to see the size picture.
+2. Choose scope: full pack, `--include` globs, or `--compress` for structure-only.
+3. Write output to `/tmp/opencode/repomix-output.xml` (or `--stdout`) rather than the repo root, unless the user wants it in the project.
+4. Read the generated file (or sections of it) to answer the user's question; cite `file:line` from the original paths shown in the output.
+
+## Notes
+
+- Default output file is `repomix-output.xml` in the working directory; use `-o` to change it.
+- `--split-output 2mb` splits huge packs into numbered parts.
+- `--include-logs` / `--include-diffs` add git history and working-tree diffs to the pack.
+- Security check runs by default; only skip with `--no-security-check` if the user explicitly asks.
+- Config: a project may have `repomix.config.json`; `npx -y repomix --init` creates one.
+- Alternative integrations exist (`repomix --mcp` for an MCP server, `--skill-generate` to emit a per-repo context skill) — prefer this CLI skill unless the user asks for those.