Word SSH key management and the control node as optional in the docs

Start with the control-node and SSH passages in docs/Blueprint.md (line 3 and section 3.11), docs/design/00-Module-Contract-and-Layout.md (section 5), docs/design/04-Credentials-and-SSH-Keys.md (section 4) and docs/design/07-Backup-and-Recovery.md (section 4), then run grep -rn "control node" docs --include=*.md excluding docs/archive. Done means each hit is worded as optional with a stated local-mode fallback, the backup copy is skipped with a message when no peer is named, and the from= restriction is said to apply only when a control node exists.

Read first

• docs/design/00-Module-Contract-and-Layout.md, section 5 "Execution model"
• docs/design/04-Credentials-and-SSH-Keys.md, section 4 "SSH key design"
• docs/design/07-Backup-and-Recovery.md, section 4 "When"
• docs/Blueprint.md, sections 3.11 and 6.1

Read these before starting. If this issue and the spec disagree, the spec wins; say so in the pull request.

Summary

Local mode, Labyrinth run on each host by itself, is the standard. Some design text still reads as if a control node and SSH key management are always there: keys restricted to the control node, backups copied to it, scans run from it. Both are useful but optional. Reword these places so they read as options, and say what happens without them.

Depends on

Nothing.

Location & Context

At main 1b0cb6c:

• docs/Blueprint.md line 3: "a rapid, idempotent, multi-OS hardening and deception deployment system".
• docs/Blueprint.md section 3.11 (line 276): off-host copies go "to the control node, or another team host named as the backup peer".
• docs/design/00-Module-Contract-and-Layout.md section 5 (line 208 on): remote mode is "built after local mode", but nothing says it is optional.
• docs/design/02-Packages-and-Third-Party-Tools.md section 6 (line 72): nmap runs "from the control node".
• docs/design/04-Credentials-and-SSH-Keys.md section 4 (lines 102 and 105): from="<control node>" restrictions, and private keys kept on the control node.
• docs/design/07-Backup-and-Recovery.md section 4 (lines 50, 62 and 70): the copy off the host goes to the control node or the backup peer, and is "required".

Current Behavior

A reader takes the control node and SSH key setup as part of every install, so the docs seem to require a central machine that local mode does not need. Where a feature depends on one (an off-host backup copy, a key restricted to a source), the docs do not say what Labyrinth does when there is none.

Plan

1. In each place listed, word the control node and SSH key management as optional ("where a control node is used").
2. For each feature that relies on them, state the local-mode behavior. For example, the backup copy goes to the backup peer when one is named; otherwise it is skipped and the run says so. The from= restriction is added only when a control node is configured.
3. Reword the Blueprint's opening line so it does not call Labyrinth a deployment system.
4. Search docs/ (not docs/archive/) for other "control node" and SSH wording that assumes them, and fix it the same way.
5. Rebuild the site locally only if needed to check links. Change wording only, and keep the meaning otherwise.

Acceptance tests

• grep -rn "control node" docs --include=*.md (outside docs/archive/): every hit is either in remote-mode text or worded as optional.
• Every feature that names the control node also says what happens without one.
• The site build and CI's link checks pass.

Done when

The design docs read as local mode first. Remote mode and SSH key management are options with a stated fallback, and the pull request lists each place changed.

Out of scope

• Changing code or behavior. This is wording only.
• Designing remote mode itself (milestone "2. Remote mode").