feat: add coding-agent skill and anyBins gating

Co-authored-by: Sreekaran Srinath <ss@sreekaran.com>

skills/coding-agent/SKILL.md

@@ -0,0 +1,78 @@
+---
+name: coding-agent
+description: Run Claude Code, Codex CLI, or OpenCode via tmux for resilient coding sessions.
+metadata: {"clawdis":{"emoji":"🧩","requires":{"bins":["tmux"],"anyBins":["claude","codex","opencode"]}}}
+---
+
+# Coding Agent (tmux-first)
+
+Use **tmux** for all coding-agent CLIs. Keep sessions resumable and logs visible.
+
+## Quick preflight
+
+```bash
+command -v claude codex opencode tmux
+```
+
+If none of `claude`, `codex`, `opencode` exist, stop and ask to install.
+
+## tmux baseline
+
+```bash
+# Create or attach
+tmux new -A -s coding-agent
+
+# Split panes
+tmux split-window -h
+tmux split-window -v
+
+# Leave running, detach
+tmux detach
+```
+
+## Claude Code
+
+Interactive (preferred in tmux):
+- `claude` — start session
+- `claude -c` — continue most recent
+- `claude -r ""` — picker
+- `claude -r <session_id>` — resume specific
+
+## Codex CLI
+
+One-shot (safe in tmux):
+- `codex exec "Write a Python function that ..."`
+- `codex exec --model gpt-4o "Complex task"`
+- `codex exec --model o3 "Reasoning-heavy task"`
+
+Interactive:
+- `codex "Your prompt"`
+- `codex resume`
+- `codex resume --last`
+- `codex resume --session <id>`
+
+Apply changes:
+- `codex apply`
+
+## OpenCode
+
+One-shot:
+- `opencode run "Write a Python function that ..."`
+- `opencode run -m anthropic/claude-sonnet-4-5 "Complex task"`
+- `opencode run -m openai/gpt-5.2 "Coding task"`
+- `opencode run -m google/gemini-2.5-pro "Research task"`
+
+Interactive:
+- `opencode`
+- `opencode -c`
+- `opencode -s <session-id>`
+
+Session management:
+- `opencode session list`
+- `opencode export [sessionID]`
+- `opencode import <file>`
+
+## Notes
+
+- Prefer **tmux** even for one-shot runs; keep history + recovery.
+- For auth, run the tool’s login flow in tmux (`claude`, `codex login`, `opencode auth`).