feat(i18n): add internationalization to TUI and Web

[sthbryan]

Changes

• Add i18n.T() and i18n.TF() functions for translated strings with format placeholders
• Add 50+ translation keys for TUI and CLI messages in English and Spanish
• Update all TUI Go components to use i18n (model_types, view, form, keyhandlers, tunnel_item, help_bar, list views)
• Update CLI startup and uninstall messages
• Add i18n to Web components (DeleteModal, EditConnection, NotificationPermission, SettingsToggle, Toasts, Dropdown, ThemeSelector, settings page)

[Copilot]

Pull request overview

Adds a shared internationalization layer across the Go TUI/CLI and the Svelte web UI, including language persistence in settings and an API endpoint to serve translations to the web frontend.

Changes:

• Introduces a Go internal/i18n package with embedded YAML locales (en/es) and formatting helpers, plus config support for a persisted language.
• Adds /api/i18n (and related) web endpoints and updates Svelte pages/components to render all user-facing strings via i18n, including a language selector in Settings.
• Refactors many TUI/CLI strings to use i18n keys and adds a web build step change.

Reviewed changes

Copilot reviewed 47 out of 47 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
web-svelte/src/routes/settings/+page.svelte	i18n-driven Settings UI + language selector
web-svelte/src/routes/+page.svelte	Localized toast messages on delete
web-svelte/src/routes/+layout.svelte	Initializes web i18n on mount
web-svelte/src/lib/stores/settings.svelte.ts	Adds language to settings state
web-svelte/src/lib/i18n/index.ts	New Svelte i18n store + translator
web-svelte/src/lib/components/TunnelCard.svelte	Localizes tunnel card UI strings
web-svelte/src/lib/components/Toasts.svelte	Localizes toast close aria-label
web-svelte/src/lib/components/ThemeSelector.svelte	Localizes “Current theme” label
web-svelte/src/lib/components/ThemeButton.svelte	Minor class update (cursor)
web-svelte/src/lib/components/SettingsToggle.svelte	Localizes enable/disable aria-label
web-svelte/src/lib/components/NotificationPermission.svelte	Localizes notification permission UI
web-svelte/src/lib/components/NewConnection.svelte	Localizes new connection form + toasts
web-svelte/src/lib/components/Header.svelte	Localizes app name/tagline + settings aria
web-svelte/src/lib/components/EditConnection.svelte	Localizes edit connection form + toasts
web-svelte/src/lib/components/Dropdown.svelte	Adds i18n defaults for dropdown labels
web-svelte/src/lib/components/DeleteModal.svelte	Localizes delete confirmation modal
web-svelte/src/lib/components/ConnectionsPanel.svelte	Localizes connections panel empty/loading
web-svelte/src/lib/api/index.ts	Exports Settings type
web-svelte/src/lib/api/endpoints/settings.ts	Adds language to Settings API type
scripts/build-web-assets.sh	Runs bun install before build
internal/web/handlers.go	Routes /api/i18n endpoints
internal/web/handlers_settings.go	Adds language setting + i18n JSON endpoints
internal/i18n/locales/es.yaml	New Spanish translations
internal/i18n/locales/en.yaml	New English translations
internal/i18n/i18n.go	New core i18n store + helpers
internal/i18n/helpers.go	Provider/status/notification helper translators
internal/i18n/embed.go	Embeds locale YAMLs + load helpers
internal/config/config.go	Persists language in config
internal/app/view.go	Localizes TUI loading/status messages
internal/app/update.go	Localizes download/status feedback
internal/app/ui/views/settings.go	Localizes settings view + language selector
internal/app/ui/views/logs.go	Localizes logs view header/hints
internal/app/ui/views/list.go	Localizes list view headers/messages
internal/app/ui/views/form.go	Localizes form labels/hints/buttons
internal/app/ui/views/empty.go	Localizes empty state copy
internal/app/ui/views/downloading.go	Localizes downloading/install UI
internal/app/ui/components/tunnel_item.go	Localizes tunnel list item status/badges
internal/app/ui/components/help_bar.go	Localizes help bar shortcuts
internal/app/ui/components/detail_panel.go	Localizes detail panel labels/actions
internal/app/model.go	Localizes install failure error message
internal/app/model_types.go	Localizes list item description text
internal/app/keyhandlers_settings.go	Adds language cycling + persistence
internal/app/keyhandlers_list.go	Localizes list actions + errors
internal/app/form.go	Localizes validation + success messages
internal/app/app.go	Loads translations + initializes language
desktop/main.go	Removes embed directive for desktop assets
cmd/ftm/main.go	Localizes CLI output strings

Comments suppressed due to low confidence (2)

web-svelte/src/lib/components/Dropdown.svelte:38

• ariaLabel/label defaults are computed once from t("options") during props destructuring, so they won’t update when the language changes. Prefer deriving a computed label reactively (e.g. const computed = $derived(label ?? t('options'))) and use that in the template, or default to undefined and translate at render time.
  cmd/ftm/main.go:56
• i18n.T/TF are used before app.New() is called (e.g. --version and --uninstall paths), but translations are only loaded inside app.New() right now. This means these code paths will print raw keys (and formatted strings will be wrong). Initialize i18n (load translations and set language) before any early-return flag handling that uses it.

func main() {
	var (
		webOnly     = flag.Bool("web", false, "Start web dashboard and open browser")
		server      = flag.Bool("server", false, "Start web dashboard only (no browser)")
		port        = flag.Int("port", 0, "Web server port (auto-detect if not specified)")
		showVersion = flag.Bool("version", false, "Show version")
		uninstall   = flag.Bool("uninstall", false, "Uninstall ftm")
	)
	flag.Parse()

	if *showVersion {
		fmt.Println(i18n.TF("version_output", version.Version))
		os.Exit(0)
	}

	if *uninstall {
		doUninstall()
		os.Exit(0)
	}

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