fix: change default viewer from rerun-web to rerun (dimos-viewer)

[spomichter]

Changes the default viewer from rerun-web (browser dashboard) to rerun (native dimos-viewer window).

The web dashboard is still available via --viewer rerun-web or VIEWER=rerun-web.

2 files changed — GlobalConfig default + docs

Depends on: #1477 (merged ✅)

[greptile-apps]

Greptile Summary

This PR changes the default viewer_backend in GlobalConfig from "rerun-web" (browser dashboard) to "rerun" (native dimos-viewer window), and updates the documentation in docs/usage/visualization.md to reflect the new default.

Changes:

• dimos/core/global_config.py: Default value of viewer_backend changed from "rerun-web" to "rerun". The change is type-safe — "rerun" is already a valid member of the ViewerBackend Literal alias.
• docs/usage/visualization.md: Quick-start comments and env-variable examples reordered and rewritten to list the native viewer first as the default, with the web viewer as an explicit opt-in.

Behavioral impact: This is a breaking change for users running dimos run in display-less environments (Docker, CI, remote servers) that previously relied on the web default. Users in headless environments will now need to explicitly pass --viewer-backend rerun-web to maintain their setup, as the native rerun viewer requires a display connection.

Confidence Score: 4/5

• Safe to merge; the code change is minimal and type-correct with clear documentation updates. Only risk is the silent breaking-default behavior for headless/display-less users who previously relied on rerun-web without an explicit flag.
• The code change is a single-line default update to a well-typed config field — no logic errors, no regressions in the type system. Documentation is updated consistently. The small deduction is for the breaking-default behavior for headless users who previously relied on rerun-web being the default without any explicit flag. Recommend noting this in release notes for existing users.
• No files require special attention beyond recommending a release note callout for headless-environment users.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[dimos run] --> B{viewer_backend set?}
    B -- No --> C["Default: rerun (native dimos-viewer)"]
    B -- Yes: rerun --> D[Open native dimos-viewer window]
    B -- Yes: rerun-web --> E[Open browser dashboard at localhost:7779]
    B -- Yes: foxglove --> F[Foxglove bridge at ws://localhost:8765]
    B -- Yes: rerun-connect --> G[Connect to existing Rerun instance]
    B -- Yes: none --> H[Headless / no viewer]
    C --> D

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_{Last reviewed commit: f1235eb}