chore(container-runner): tighten comments - #5589

Stack for rivet-dev/actors

• #5594 feat(container-runner): drain engine sleeps unless the idle …
• #5595 feat(container-runner): jitter idle timeout to avoid teardow …
• #5585 feat(container-runner): self-sleep on repeated actor start
• #5586 feat(container-runner): sleep on startup idle timeout
• #5589 chore(container-runner): tighten comments 👈
• #5587 feat(container-runner): exit process when the last child sto …
• #5588 feat(container-runner): drain child before SIGTERM on engine …
• #5584 feat(container-runner): drain children and engine concurrent …
• #5565 fix(envoy-client): ack terminating stop commands so pegboard …
• main

Get stack: forklift get 5589
Push local edits: forklift submit
Merge when ready: forklift merge 5589

_{change zrxxyxls}

Review

This is a documentation/comment-only change (chore(container-runner): tighten comments). I diffed every hunk and confirmed no executable Rust code lines were touched, only //////!/// doc-comments, README/Dockerfile/YAML/shell comments, and prose in container-runner/README.md. No behavior change, so no new test coverage is needed for this PR.

Code quality

• The trims are good: they collapse multi-sentence doc-comments into tighter prose without losing the load-bearing "why" (e.g. the stop_child/drain_then_stop_child/SIGTERM_BUDGET comments in main.rs and actor.rs still explain the non-obvious invariants, just more concisely).
• monitor.rs's module doc-comment removal of the per-source bullet list is safe: the detail now lives on MemSource/CpuSource variant doc-comments (verified those exist with matching content), so nothing was actually lost, just de-duplicated.
• Consistent with CLAUDE.md's comment-style rules: em dashes are gone from all added lines, and I did not find any newly-introduced fragmented parenthetical-dash constructions in the added code comments.

Naming: "Cloud Run" to "serverless"/"Rivet Compute"

• These renames read correctly in context (e.g. docker-compose.yml, run-host-loadtest.sh, Dockerfile, server.mjs). One pre-existing "Cloud Run" mention remains in container-runner/examples/unity-demo/Dockerfile:5 ("Compute (or any container host: Cloud Run, Fly, a VM, etc.)"), but that one is an example list of generic hosting options, not a reference to Rivet's own platform, so leaving it as-is is fine and not a gap in this PR.

Bugs / correctness
None found. This is a pure comment/prose change with no logic touched.

Performance / security
Not applicable; no code paths changed.

Test coverage
Not applicable; comment-only diff.

Overall: clean, low-risk cleanup. No changes requested.