i18n: English-first interface, plus CI/CD for Linux, Windows and Android

[Wasabules]

Converts the whole project to an English-first interface translated at
runtime, and adds the CI/CD needed to ship it.

i18n

No user-facing string is written inline anymore. English is the source
language; French ships as a translation and falls back to English key by key,
so a partial translation degrades gracefully instead of showing raw
identifiers.

Go no longer sends display text across the Wails boundary. app.go emits
Message{Key, Args} values and the frontend renders them from its own
catalogue, so a string exists in exactly one place rather than being
translated on both sides where the copies would drift apart. A consequence
worth knowing: switching language re-renders the whole log retroactively,
because the lines were never text to begin with.

Catalogue	Covers
frontend/src/locales/*.json	everything inside the window (141 keys)
internal/i18n/locales/*.json	desktop notifications, peatsctl (58 keys)
android/.../values*/strings.xml	the Android app (67 strings)

The Svelte i18n module is ~60 lines with no npm dependency. It supports linked
messages: an argument value prefixed with @: is itself a catalogue key,
which keeps a nested reason translated inside a sentence Go assembled
("Reconnect 2/10: control channel busy").

The desktop app detects the system language, offers a picker in the top bar,
remembers the choice and reports it to Go, so a notification never arrives in
a different language from the window that triggered it. Android follows the
system language through resource qualifiers.

Docs are English only, except README.fr.md. PROTOCOL.md is deliberately
not translated: duplicating a 20 kB reference means maintaining two that
eventually disagree.

CI/CD

ci.yml — Go vet and tests on Linux and Windows (the two transports share no
code, so a build error in one is invisible from the other), the probe module,
catalogue consistency, the frontend build, and an Android debug build.

release.yml — cut from a v* tag, produces .deb / .tar.gz / peatsctl,
an NSIS installer / portable .zip / peatsctl.exe, and .apk / .aab,
with SHA256SUMS. Versions derive from the tag everywhere. Android signing is
optional: with no secrets configured the workflow still produces an unsigned
APK rather than failing.

Three checkers keep the catalogues honest — missing keys, dead keys and
mismatched {placeholders} all fail the build. They already caught a
mis-sorted key while being written.

Also fixed along the way

• probe/main.go now declares the //go:build linux constraint it always
  needed; without it the package failed to typecheck anywhere else.
• The Windows transport no longer claims to be untested — it was validated on
  hardware.

Verified locally

gofmt, go vet, go test, the three catalogue checkers, the frontend
build, a full application build with embedded assets, and peatsctl -lang fr
rendering its help in French. The Android build was not run locally (no SDK
here); instead every one of the 67 R.string references was checked against
the resources.

🤖 Generated with Claude Code