fix(help): recommend a resolvable model and label bare rocm as the launcher (EAI-8011)

[fredespi]

Summary

Two help-text defects surfaced by the README walkthrough (EAI-8011), fixed in apps/rocm/src/main.rs. Help/doc text only — no behaviour change.

• The worked serve examples named a model the CLI cannot resolve. rocm serve qwen2.5-7b-instruct is neither a catalog name nor an owner/repo reference, so copying an example verbatim fails. Replaced all six help/doc occurrences with qwen, a real catalog alias for the built-in assistant (Qwen3-4B-Instruct-2507-GGUF) that rocm model resolves. Realigned the top-level EXAMPLES column for the shorter name.
• The help described bare rocm as opening the dashboard — the same thing it says rocm dash does. Running rocm with no subcommand actually opens the launcher (launch_default → run_launcher), so the long_about now says "interactive launcher (TUI)". The dash command's own help row still describes the dashboard, so the two read distinctly.

These are the two EAI-8011 rows pinned as expected failures in #241; once both land those rows XPASS and retire themselves.

Test plan

• Built rocm on Linux (macOS can't build this repo — known platform-gated st_mode failure in rocm-engine-lemonade).
• Ran rocm help, rocm serve --help, rocm model --verbose against the built binary at wide terminal width; confirmed every rocm serve example names qwen (listed in model --verbose as aliases=[qwen, ...]) and the no-subcommand sentence no longer says "dashboard" while the dash row still does.
• Linux workspace gate (clippy + full test suite) green apart from an unrelated full-disk environment failure.

[r0x0r]

Reviewed. Doc/help-text only, no behaviour change, and both fixes check out against the code:

• qwen is a real, resolvable catalog alias — BUILTIN_ASSISTANT_MODEL_ALIAS = "qwen" maps to Qwen3-4B-Instruct-2507-GGUF (apps/rocm/src/providers.rs), so every replaced rocm serve qwen / rocm chat --model qwen example now names something the CLI can actually resolve, unlike the previous qwen2.5-7b-instruct.
• The long_about wording change is accurate: bare rocm routes to launch_default → run_launcher (the launcher/TUI), and the distinct dash row still describes the dashboard, so the two no longer read identically.

All six occurrences are consistent and the EXAMPLES column realignment looks right. No substantive concerns.

[r0x0r]

Approving. The two EAI-8011 help-text defects are fixed correctly: every serve/chat example now names qwen, a real resolvable alias (BUILTIN_ASSISTANT_MODEL_ALIAS -> Qwen3-4B-Instruct-2507-GGUF), and the bare-rocm long_about now accurately says launcher (launch_default -> run_launcher) while the dash row still describes the dashboard. Doc-only, no behaviour change, 24/24 CI green.