fix(desktop): stop portable launchers from persisting bind overrides into config.json

[fengyue-xve]

Summary

Fixes #1816. octop run --host/--port persists the CLI overrides into config.json by design, but the desktop exe and the portable launchers passed their own defaults as flags on every start, so a hand-edited bind_host reverted to 127.0.0.1 the moment the app restarted.

• desktop/src/process.go: the spawned launch.py run no longer carries --host 127.0.0.1 --port <port> flags. The same values are passed as OCTOP_BIND_HOST / OCTOP_PORT env entries, which resolve_bind honors (env > config.json) and never writes back. The desktop still binds loopback exactly as before, so no behavior changes beyond persistence.
• desktop/portable/templates/start.bat / start.sh: --host/--port are now forwarded only when the user passed them explicitly (documented octop run flag semantics preserved). A plain launch passes neither, so the bind comes from config.json and the file is left untouched. The status line now says when values come from config.json instead of printing a possibly-wrong default URL.
• The help text of both launchers reflects that config.json is the default source.

Target branch

• Base is develop (feature / fix — default)

Type of change

• Bug fix

Test plan

• No local Go toolchain is available in this environment (go is not installed / cannot be executed), so the process.go change is verified by inspection + CI/manual; it only replaces argv flags with env entries on the same exec.Command.
• uv run pytest tests/unit/cli/test_run_bind_resolution.py — passed, including the new test_env_overrides_do_not_touch_config_file which runs octop run with OCTOP_BIND_HOST/OCTOP_PORT set and asserts config.json keeps its original bytes (no "Saved config", uvicorn gets the env values).
• uv run pytest tests/unit/desktop/test_portable_launcher_argv.py — 3 passed. The tests run the real start.sh with a stubbed portable Python: a default launch executes launch.py run with no --host/--port at all, while explicit flags are still forwarded. Red→green: on the unpatched script the first and third cases fail because the defaults are always appended.
• ruff check / ruff format --check on the changed test files — clean.
• Added/updated tests

Checklist

• Updated CHANGELOG.md (if user-facing)

[fengyue-xve]

Heads-up: develop currently has two unrelated repo-level CI failures that also surface on this PR. (1) The Linux job flakes on test_cold_target_install_budget_preserves_regular_timeout — fixed by #1826. (2) The Windows job fails on two plan-path tests introduced by #1825 — fixed by #1841. Neither comes from this change.