feat: add HarmonyOS OpenHarmony support

Harvest the HarmonyOS/OpenHarmony port from PR #2634 and make it publish-safe by target-gating unsupported host dependencies out of the OHOS TUI graph. Self-update is disabled on OHOS, PTY shell mode reports unsupported, and Starlark execpolicy parsing returns an explicit unsupported-platform error until upstream starlark/rustyline/nix support catches up.

Add OHOS SDK setup docs and launcher scripts, install the rustls ring provider for rustls-no-provider entrypoints, and keep the packaged codewhale-tui OHOS graph free of starlark, rustyline, nix@0.28, portable-pty, and arboard.

Validation: cargo fmt --all -- --check; git diff --check; git diff --cached --check; cargo check -p codewhale-cli --locked; cargo check -p codewhale-app-server --locked; cargo check -p codewhale-tui --locked; cargo test -p codewhale-cli --locked update::tests::; cargo test -p codewhale-release --locked; cargo test -p codewhale-tui --locked background_tty_command_has_controlling_terminal; cargo test -p codewhale-tui --locked clipboard; cargo package -p codewhale-tui --allow-dirty --no-verify --locked; packaged OHOS cargo tree checks. OHOS target check still requires a loaded OpenHarmony SDK/sysroot and currently stops in ring with missing assert.h when CC/CFLAGS/linker are unset.

Harvested from PR #2634 by @shenjackyuanjie.

Co-authored-by: shenjackyuanjie <54507071+shenjackyuanjie@users.noreply.github.com>

.gitignore

@@ -50,6 +50,8 @@ docs/*.pdf
 # Local dev scripts and temp files
 *.sh
 *.cmd
+!ohos-clang.sh
+!ohos-clangxx.sh
 !scripts/**
 !.github/scripts/**
 test.txt