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>

.cargo/config.toml

@@ -0,0 +1,18 @@
+# HarmonyOS/OpenHarmony cross-build paths are intentionally not configured
+# here. Cargo does not expand environment variables inside target linker paths
+# or CMake toolchain paths, so checked-in absolute SDK paths make the workspace
+# machine-specific.
+#
+# See docs/HarmonyOS.md for setup details.
+#
+# Set OHOS_NATIVE_SDK to the OpenHarmony native SDK directory, then load one of:
+#
+#   PowerShell:
+#     . .\scripts\ohos-env.ps1
+#
+#   Linux/macOS:
+#     . ./scripts/ohos-env.sh
+#
+# The setup scripts export Cargo's target-specific linker, AR, CC, CXX, CFLAGS,
+# CXXFLAGS, CARGO_ENCODED_RUSTFLAGS, CC_SHELL_ESCAPED_FLAGS, and
+# CMAKE_TOOLCHAIN_FILE variables for aarch64-unknown-linux-ohos.