docs(aspire): expose detached non-TTY start state and dashboard-token discovery

[rickylabs]

Summary

Residual documentation work from #1306: headless agents still need an explicit, supported way to locate detached aspire start state and discover the dashboard token without guessing files or duplicating inventory commands.

Acceptance

• Document where non-TTY/detached aspire start records its live state and how callers distinguish started, exited, and stale sessions.
• Document the supported dashboard-token discovery path for headless automation without printing secrets into ordinary logs.
• Reuse the canonical Aspire inventory/describe surface; do not add a second competing process inventory command.
• Add a runnable documentation or CLI fixture proving both paths.

Boundary

#1306 is complete because its acceptance rows were alternative remedies. This follow-up owns only the two useful residual documentation surfaces and is intentionally outside 0.0.7.