upstream(sync): Mobile UI — upstream 0.5.12–0.5.18 parity

[devin-ai-integration]

Summary

Takes upstream Buzz mobile/ wholesale from desktop-v0.5.11 → desktop-v0.5.18 and re-homes Crew's mobile delta on top of it. Per issue #277's conflict matrix, mobile/ is low-conflict and Crew's fork divergence there is small, so this is a tag-scoped port rather than a per-PR cherry-pick.

Upstream scope landed: compact permalink chips (block#5639), community invites (block#5641), composer input regressions (block#5594), profiles/DMs/sheets polish (block#5401), timeline/composer/emoji work (block#5645, block#5873, block#5874, block#6297), thread tail + iOS channel header (block#6399), device auth for identity export (block#5116), batched observer telemetry unwrap (block#5805), pairing confirmation (block#6018), iOS native emoji picker (block#5853), channel details page (block#6113).

Crew divergence preserved (the only Crew-owned mobile delta that survives):

• features/channels/agent_activity/** (agent activity line, observer control/models, working-bot providers) and shared/relay/** observer plumbing are kept.
• AgentActivityLine stays mounted above both composers, now nested inside upstream's new AndroidImeLift composer dock:

AndroidImeLift(child: ... ComposerDockSizeReporter(child: Column(children: [
  ChannelTypingIndicator(...),   // upstream
  AgentActivityLine(...),        // Crew
  ComposeBar(...),               // upstream
])))

• Upstream moved features/profile/user_cache_provider.dart + user_profile.dart → shared/profile/; Crew's agent-activity imports were re-pointed at the new location rather than keeping a duplicate.
• Channel-first IA (upstream(sync): Guardrail — preserve channel-first IA during 0.5.18 merge #278) is untouched — no Projects rail / Workbench / top-nav Projects concept exists in mobile/ and none was introduced.

docs/crew/upstream-buzz.json is intentionally not bumped here: the pin belongs to the meta sync issue #285 and bumping it from a mobile-only child PR would claim parity this PR does not deliver on its own. docs/crew/STATE.md is updated to record that mobile is now in scope for upstream sync (the earlier "mobile out of scope" decision is superseded); D-026 is unchanged — desktop remains the main office.

Related issue

Fixes #277 (child of #285; guardrails per #278).

Testing

TDD order, evidence attached in the session:

Stage	Result
Baseline flutter test on pre-port code	1307 passing
Upstream tests ported, before implementation (RED)	699 passing / 70 failing
After implementation (GREEN)	1575 passing / 0 failing

Mobile checks: flutter analyze → 0 issues; dart format --set-exit-if-changed clean; file-size ratchet clean.

Gates run individually (not just ci — its mobile dart format leg hangs in this env):

• pnpm --filter buzz check — pass
• pnpm --filter buzz typecheck — pass
• pnpm --filter buzz test — pass
• just test-unit — 4 pre-existing failures unrelated to this diff: buzz-cli command_inventory_is_stable, subcommand_counts_are_stable, subcommand_names_are_stable and buzz-db migration::tests::embedded_migrator_contains_consolidated_initial_schema. Reproduced identically from a clean main worktree (logs 11-preexisting-main-buzz-cli.log, 12-preexisting-main-buzz-db.log). Everything else passes.
• just check-compile — N/A, no Rust changes in this diff (just _ensure-sidecar-stubs verified anyway).

UI evidence — full-screen Android emulator (1080x2400, xyz.block.buzz.mobile), clean main build vs. this branch's build:

Before (main / 0.5.11)	After (this branch / 0.5.18)

Limitation, stated rather than papered over: every surface this port changes (timeline, composer, emoji picker, thread tail, channel details, invites, pairing confirmation) lives behind device pairing, which needs a paired desktop + live relay that this environment cannot stand up. So the emulator screenshots prove the ported app builds, installs and launches unchanged through the pairing wall, and the 1575-test widget suite (which pumps those exact widgets, including the new upstream ones) is the behavioural evidence for what is behind it.

Link to Devin session: https://app.devin.ai/sessions/51e0224f24344b1ea587ded6909157a3
Requested by: @oscarlehuu

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