Add preview states for RuntimesScreen with various connection statuses

[harshjainnn]

Summary

Replaces the generic RuntimesScreenPreview in RuntimesScreen.kt with 6
state-specific Compose previews covering the major runtime manager/adapter
states (connected, connecting, auth failed, disabled manager, no runtime
configured, degraded). Adds a fakeRuntimesState() helper to build
deterministic mock state for each preview. Closes #37 .

This is a UI-only change — no runtime protocol, adapter behavior,
authentication, or settings persistence logic was touched.

Validation

• ./scripts/check.sh
• git diff --check
• Device test, if relevant: N/A — Compose preview-only change, no runtime/device logic touched
• Screenshot, trajectory, audit export, or release artifact evidence, if relevant: previews render correctly in Android Studio / Compose preview pane for all 6 states

Risk

• No API keys, private SSH keys, signing keys, generated build artifacts,
  personal device data, or proprietary vendor files are included.
• Licensing impact reviewed for any new third-party material.
• Privacy/security impact reviewed for assistant, watcher, background-run,
  audit, model-provider, or device-control changes.
• Docs updated for user-visible behavior, build flow, or release process
  changes.

Contributor Agreement

• I have read and agree to CONTRIBUTING.md, including
  the contributor assignment/license/no-compensation terms.
• I have the right to submit this contribution under those terms.
• This contribution does not include material I am not allowed to submit.

[vercel]

@harshjainnn is attempting to deploy a commit to the adam-7512's projects Team on Vercel.

A member of the Team first needs to authorize it.

[adamcohenhillel]

Reviewed the preview-only RuntimesScreen change and ran local repo validation in an isolated worktree: ./scripts/check.sh and git diff --check both passed.

[adamcohenhillel]

Reviewed against latest origin/main (906a9123) in an isolated worktree. This PR still merges cleanly and remains a useful preview-only improvement for #37.

Local validation after merging the PR onto current main:

• ./scripts/check.sh passed
• git diff --check origin/main..HEAD passed

I am intentionally not merging this because the PR is not authored by adamcohenhillel. Remaining note: the Vercel status is still failing due to external-contributor deployment authorization, not because of a docs build failure shown in the PR metadata.