LATU: add a generic dual-translator status manager

[LaurenIsACoder]

Summary

• add an independent latu-runtime-manager command; no overlapping latu wrapper is installed
• report latx-x86_64 and latx-i386 separately through a stable, distribution-neutral status contract
• support translators installed through alternatives or other valid executable symlinks
• keep this layer limited to translator facts; runtime readiness, catalog selection, and provisioning remain follow-up work
• install the manager through Meson and exercise it in every existing LoongArch CI container

Behavior

$ latu-runtime-manager status
translator_x86_64=present
translator_i386=missing

Each value is present, missing, or unknown. unknown means the selected translator path could not be inspected safely, such as a root escape. status exits successfully when either translator is absent or unknown because those are query results, not command failures. Invalid arguments or an invalid --root return status 2. --root ROOT exists for inspecting a filesystem tree and tests; normal host use does not require it.

In normal host mode, the manager resolves its own final symlink before probing sibling translators, so invocation through /usr/local/bin or an alternatives-style link still inspects the actual installation directory. A translator symlink is present when its resolved target is a regular executable file.

In --root mode, translator symlinks are followed only when their resolved targets remain inside the selected root. A symlink that escapes the root or cannot be resolved safely is reported as unknown, not missing or present.

The implementation does not read os-release, branch on ID or ID_LIKE, contain a distribution allowlist, or infer runtime readiness from translator presence. Distribution names occur only in the existing CI image matrix, where they identify test environments.

Series

• PR1: LATX: support dual-target loader prefixes in release builds #365 — user-scoped loader-prefix configuration for both translators
• PR2: this PR — independent dual-translator status foundation
• PR3: LATX: report runtime selection and guide loader failures #370 — translator runtime information and missing-runtime guidance

PR1 and PR2 can be reviewed and merged in either order. PR3 is now published as a draft for early review; it should not be merged until both foundations are accepted.

Commit structure

1. runtime: report both LATX translators — command contract and focused source-tree matrix
2. build: install and exercise the runtime manager — Meson installation, installed-layout regression, and CI wiring
3. runtime: support symlinked translator installs — alternatives-compatible probing, root containment, and manager-symlink discovery

Validation

• deterministic RED: valid translator symlink was reported missing
• deterministic RED: a translator symlink escaping --root was incorrectly reported present
• deterministic RED: manager invocation through a symlink probed the alias directory instead of the actual installation directory
• GREEN on macOS: complete source-tree dual-translator matrix passed, including all three symlink regressions
• GREEN on native LoongArch: source-tree matrix passed at commit 4bc4146f89a
• native LoongArch product builds with tests disabled: latx-x86_64 and latx-i386 passed
• native LoongArch installed-layout tests passed for both x86_64 and i386 build trees
• native LoongArch focused Meson tests: 2/2 passed for both x86_64 and i386 build trees
• native LoongArch lat-pr-fast: x86_64 13/13 and i386 6/6 passed
• installed-layout tests verify the configured bindir, sibling discovery, both output keys, and absence of a generated latu command
• native release packaging passed; the archive contains latu-runtime-manager, latx-x86_64, and latx-i386
• sh -n runtime/latu-runtime-manager tests/runtime/test-latu-runtime-manager.sh
• git diff --check
• checkpatch: 0 errors; only the expected new-file/MAINTAINERS warnings