feat(mobile): rebase iOS PR #17 onto main + scaffold Flutter→RN migration

[matej21]

What this is

Two layers on one branch:

1. PR feat/ios #17 (feat/ios) rebased onto current main. PR feat/ios #17 was ~242 commits behind main and CONFLICTING. This branch replays it on top of current main (5 desktop conflicts resolved + one post-rebase API fixup). Builds and tests pass.
2. Start of the Flutter → React Native migration (uniffi + native Skia rendering, no xterm.js), per mobile/RN_MIGRATION.md.

Closes the rebase need of #17; the RN work is additive and does not touch the desktop app.

Layer 1 — rebased iOS/mobile work (from #17)

Conflicts resolved against main's evolution:

• okena-terminal/.../resize.rs — terminal.rs was split into a terminal/ dir in main; the min-1 col/row clamp was re-applied in the new location.
• remote_commands.rs — combined main's api_project_visibility with feat/ios #17's to_api_with_sizes (terminal sizes in state).
• navigation.rs — semantic merge of main's multi-window + FocusManager with feat/ios #17's tab-aware navigation.
• views/window/{mod,render}.rs — took main's side; dropped feat/ios #17's desktop "ensure-visible vs center scroll" tweak (it renamed a field main references in 5 other places; unrelated to mobile).
• fix(rebase): deregister_pane_bounds gained a window_id arg in main; adapted the tab-container callsite.

Verified: cargo check -p okena -p okena_mobile_native ✅ · cargo test -p okena-terminal -p okena-layout → 92 passed ✅

Layer 2 — React Native migration (Phase 1–2 scaffold)

• mobile/RN_MIGRATION.md — the plan: keep okena-core + alacritty, swap the binding (flutter_rust_bridge → uniffi/ubrn, JSI), render the terminal natively via react-native-skia. xterm.js explicitly rejected. Documents the hot-path packed-buffer bridge and a "drop Rust" fallback.
• crates/okena-mobile-ffi — uniffi binding crate (uniffi 0.29, 61 exports) that reuses okena_mobile_native's ConnectionManager/handler/holder verbatim (no logic duplication; its crate-type gains "lib"). Adds get_visible_cells_packed() (compact LE cell buffer for the renderer). cargo check passes for it and okena_mobile_native (Flutter Rust side intact).
• mobile/rn/ — the RN app: a typed OkenaNative binding contract + packed-cell decoder, a Skia TerminalView (3-pass paint ported from terminal_painter.dart), zustand state stores (ported from the Flutter providers), models, navigation, persistence, and the screens/widgets (ServerList, Pairing, Workspace, ProjectDrawer, KeyToolbar, LayoutRenderer, TerminalPane). All 15 Flutter app source files have an RN counterpart. Verified: npm install + npx tsc --noEmit (strict) pass over all 22 RN source files.

Not done yet (honest status — why this is a draft)

• Never built/run on a device. No Android/iOS SDK here, and the ubrn-generated native module is not wired — getOkenaNative() throws until it is. So this is a structurally-complete, type-checked port, not a proven-equivalent running app.
• TLS is a no-op in the uniffi connect() — client-side TLS lives on arch-review-fixes (PR Architecture review fixes: PTY starvation, persistence durability, remote/mobile leaks #134), not on main. Forward-compatible signature is in place.
• Dart tests not ported (layout_node_test, saved_server_test, terminal_flags_test, widget_test); no RN test runner yet.
• Deliberate adaptations: clipboard write, swipe-delete→long-press, split-divider drag-resize, SafeArea, and per-cell metrics are simplified/omitted (spike-level). Build tooling (cargokit) is replaced by ubrn, not ported.

Next steps (require a local RN toolchain)

1. ubrn build android/ios --and-generate over crates/okena-mobile-ffi; replace getOkenaNative()'s body with the generated module (mobile/rn/README.md has exact commands).
2. Run on device → validate the Skia renderer holds 60fps (Phase 0 spike S2).
3. Wire TLS once PR Architecture review fixes: PTY starvation, persistence durability, remote/mobile leaks #134 lands on main.

Reviewing

The diff is large because it includes the #17 rebase. The desktop/Flutter portion was reviewed in #17; the new work in this PR is the RN migration: mobile/RN_MIGRATION.md, crates/okena-mobile-ffi/, and mobile/rn/.

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