feat: add native T4 companion app for iOS and Android

[wolfiesch]

What this changes

• Add an Expo and React Native companion for the T4 attention inbox, sessions, transcripts, approvals, and host setup.
• Store one Tailnet host securely and reconnect when the app returns to the foreground or is relaunched.
• Add environment checks, physical-device workflows, explicit long-session loading states, and Phone Setup links.

This remains a draft checkpoint while an alternative Flutter client is evaluated. The server-side bounded-tail fix for transcripts larger than 64 MiB is not part of this PR.

How you verified it

On 2bd5cd2:

• mise exec node@24.17.0 -- pnpm --filter @t4-code/companion typecheck
• mise exec node@24.17.0 -- pnpm --filter @t4-code/companion test
• mise exec node@24.17.0 -- node apps/companion/scripts/doctor-node-tests.mjs
• Installed and launched a signed Release build on a physical iPhone; after relaunching with the screen locked, the app reconnected to the configured Tailnet host and reloaded sessions.

Exact-head GitHub Actions are not green: android-debug passed; core and tooling failed the same release-consistency invariant because the companion version is 0.1.29 while the repository version is 0.1.30; the aggregate verify job therefore failed.

Checklist

• pnpm check passes (release contract, provenance, lint, typecheck)
• pnpm test passes; new behavior has a test that fails without this change
• Any pasted logs or screenshots are redacted: no secrets, tokens, pairing codes, or private paths
• Ported code (T3 Code / OMP) follows the provenance rules in THIRD_PARTY_NOTICES.md (not applicable; no ported code)

[riverpilot]

Recommend closing as obsolete/superseded, not repairing for merge. Current main already ships the maintained Flutter Android/iOS/macOS client under com.lycaonsolutions.t4code; this Expo companion claims the same native identity, so the two applications cannot coexist. Rebasing also rejects Flutter's native Origin: https://localhost handshake at the Tailnet gateway and carries stale 0.1.29 release metadata that fails the 0.1.30 release contract. Preserve one supported native client: Flutter.

[riverpilot]

Maintainer recommendation: close this draft as superseded by the merged Flutter native client. Do not maintain two native apps with the same iOS/Android identity.