chore(doc): require 'path:' prefix for seedSdk

[alekseifedotov]

If the seekSdk is inside of workdir and there is no 'path:' prefix, it will fail to find the sdk

[github-actions]

No concrete correctness or merge-blocking issues found in the PR changes.

[Copilot]

Pull request overview

Updates onboarding guidance to ensure Nix reliably resolves the local Seek Thermal SDK input by requiring the path: prefix when overriding seekSdk.

Changes:

• Document using path:PATH_FROM_STEP_3 for --override-input seekSdk to avoid Nix resolving to a git repo root unexpectedly.
• Update .envrc.example to show path: usage in VENDORED_SEEK_PATH.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/src/first-time-setup.md	Clarifies the path: prefix requirement and explains the failure mode when the SDK path is inside a git repo.
.envrc.example	Updates the example SDK override variable to include the path: prefix.

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[github-actions]

No concrete correctness, security, or regression issues found in the PR changes. The documented path: prefix and quoted variable usage are consistent with Nix and direnv behavior.

[github-actions]

No concrete correctness, security, or merge-blocking issues found in the documentation-only changes.

[github-actions]

No concrete issues found. The documentation and .envrc.example consistently add the required path: prefix.