docs: expand terminal backends section + fix docs build

[teknium1]

Summary

Expands the Terminal Backend Configuration section from ~65 lines to ~170 lines with dedicated subsections for all 6 backends. Also fixes a pre-existing Docusaurus build error that was preventing site deployment.

Terminal backends documented

Each backend now has its own subsection with config yaml, requirements, persistence model, security details, and special behavior:

• Local — default, no isolation, no setup
• Docker — security hardening details (cap-drop, PID limits, tmpfs), credential forwarding, container lifecycle
• SSH — ControlMaster, persistent shell, all env vars (host, user, port, key)
• Modal — cloud sandbox, filesystem snapshots, credential file mounting
• Daytona — managed workspaces, stop/resume, 10 GiB disk cap
• Singularity/Apptainer — HPC-focused, SIF caching, scratch directory resolution, overlay persistence

Added a comparison table showing isolation level and best use case for each.

Docs build fix

Fixed pre-existing MDX compilation failure in feishu.md where bare angle-bracket URLs (<https://open.feishu.cn/>) were parsed as JSX tags. This was blocking ALL site deployments since the Feishu page was added. Converted to standard markdown links.

Docs build verified

npx docusaurus build succeeds locally.

[github-actions]

⚠️ Supply Chain Risk Detected

This PR contains patterns commonly associated with supply chain attacks. This does not mean the PR is malicious — but these patterns require careful human review before merging.

⚠️ WARNING: base64 encoding/decoding detected

Base64 has legitimate uses (images, JWT, etc.) but is also commonly used to obfuscate malicious payloads. Verify the usage is appropriate.

Matches (first 20):

3946:+                b64 = base64.b64encode(content.encode("utf-8")).decode("ascii")

⚠️ WARNING: exec() or eval() usage

Dynamic code execution can hide malicious behavior, especially when combined with base64 or network fetches.

Matches (first 20):

3732:+                home = self._sandbox.process.exec("echo $HOME").result.strip()
3891:+        content into the sandbox via exec(), so new/updated credentials are

---

Automated scan triggered by supply-chain-audit. If this is a false positive, a maintainer can approve after manual review.