feat: add inference.sh integration (infsh tool + skill) (#1682)

Add inference.sh CLI (infsh) as a tool integration, giving agents
access to 150+ AI apps through a single CLI — image gen (FLUX, Reve,
Seedream), video (Veo, Wan, Seedance), LLMs, search (Tavily, Exa),
3D, avatar/lipsync, and more. One API key manages all services.

Tools:
- infsh: run any infsh CLI command (app list, app run, etc.)
- infsh_install: install the CLI if not present

Registered as an 'inference' toolset (opt-in, not in core tools).
Includes comprehensive skill docs with examples for all app categories.

Changes from original PR:
- NOT added to _HERMES_CORE_TOOLS (available via --toolsets inference)
- Added 12 tests covering tool registration, command execution,
  error handling, timeout, JSON parsing, and install flow

Inspired by PR #1021 by @okaris.

Co-authored-by: okaris <okaris@users.noreply.github.com>

skills/inference-sh/cli/references/authentication.md

@@ -0,0 +1,59 @@
+# Authentication & Setup
+
+## Install the CLI
+
+```bash
+curl -fsSL https://cli.inference.sh | sh
+```
+
+## Login
+
+```bash
+infsh login
+```
+
+This opens a browser for authentication. After login, credentials are stored locally.
+
+## Check Authentication
+
+```bash
+infsh me
+```
+
+Shows your user info if authenticated.
+
+## Environment Variable
+
+For CI/CD or scripts, set your API key:
+
+```bash
+export INFSH_API_KEY=your-api-key
+```
+
+The environment variable overrides the config file.
+
+## Update CLI
+
+```bash
+infsh update
+```
+
+Or reinstall:
+
+```bash
+curl -fsSL https://cli.inference.sh | sh
+```
+
+## Troubleshooting
+
+| Error | Solution |
+|-------|----------|
+| "not authenticated" | Run `infsh login` |
+| "command not found" | Reinstall CLI or add to PATH |
+| "API key invalid" | Check `INFSH_API_KEY` or re-login |
+
+## Documentation
+
+- [CLI Setup](https://inference.sh/docs/extend/cli-setup) - Complete CLI installation guide
+- [API Authentication](https://inference.sh/docs/api/authentication) - API key management
+- [Secrets](https://inference.sh/docs/secrets/overview) - Managing credentials