#3243 [Docs] the 0.1.44.1 changes no page told: a crashed engine start names itself, and a setup run again keeps the installed size

Description

### Problem and result

The 0.1.44.1 changes were not in any docs page:

1. When the engine start crashes, the server now names the crash: an exit with no engine line is reported as the launcher's own "engine started" bookkeeping, so the user sees which start died (#2324).
2. A setup run on a machine that already has the parts installed keeps the installed size (it no longer re-downloads what is already there).

After: `docs/INSTALL.md`, `docs/AI_SETUP.md`, `docs/TROUBLESHOOTING.md` and the 0.1.44.1 release notes state both, matching the code. Docs-only.

### Related discussion

Closed in the 0.2.0-beta tracker reset; rebased on main and re-verified per the reset note. #2324 is the start-crash report.

### Approach

Docs text only, verified against the code on current main: the start-crash bookkeeping in `serve/server.py` (the "engine started" line plus GPU runtime failure are the launcher's own output; an exit with no line is named), and setup.py's "already installed" paths that keep the installed size on a re-run.

### Validation

Passed (static verification, rebased on 0.2.0-beta main `e88ee39d`): every doc statement re-checked against `serve/server.py` and `setup.py` on current main — the start-crash wording matches the server's launch/drain block, the keep-size wording matches setup.py's "already installed" messages.
Not run: no code change, nothing to run.

### Limits

Docs only; describes 0.1.44.1 behavior that is already shipped.