docs(research): Android participant instructions for Research Edition sideload

[TimeToBuildBob]

Summary

Adds src/research/participant-instructions-android.rst — participant-facing
install and export steps for the Android Research Edition APK, and wires it
into the research toctree.

Follows up on #181 (desktop guide, merged), which explicitly deferred Android:
"The VR Android pilot (direct APK, ~40 people, deadline 2026-09-29) will need
its own page before anyone sideloads; that is a follow-up, not this PR."

What the page covers:

• Enable "Install from unknown sources" — Android 8+ per-app path, Android 7
  global path, Oculus/Meta Quest Developer Mode for VR headsets
• Download and install the APK
• Confirm the Research Edition badge on port 5667
• Export via "Export all buckets as JSON" and upload
• Researcher notes: battery optimisation exemption, export-fails-closed rule,
  two-buckets-is-normal, fixed export filename

The page is styled to match participant-instructions.rst and ends with a
cross-reference to it.

Test plan

• sphinx-build passes without warnings on the new file
• Toctree renders the Android page alongside the desktop page
• Cross-reference :ref:\research-participant-instructions`` resolves
• Researcher notes section is accurate against v0.14.0b5-research behaviour

[TimeToBuildBob]

🤖 AI code review

Safe to merge — no P0/P1 findings

Confidence 5/5

✅ No findings. The diff looks correct to me on this pass.

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[greptile-apps]

Confidence Score: 5/5

The documentation changes appear safe to merge, with both previous findings resolved and no actionable new issue established.

Summary

Adds participant-facing instructions for installing, verifying, operating, and exporting data from the Android Research Edition, and links the page from the research documentation index.

• Covers Android and Meta Quest sideloading workflows.
• Documents Research Edition identification, data export, battery optimization, and application-data isolation.
• Revises export guidance to handle both save prompts and silent browser downloads.
• Clarifies that standard and Research installations have separate storage while imported data can still enter the Research database.

_{Reviews (2) · Last reviewed commit: "docs(research): clarify Android export s..."}

[TimeToBuildBob]

@greptileai review