feat(launcher): route all UI strings through t(key) indirection

strings.lua holds English defaults. ctx.t(key, ...) looks up the key,
optionally string.formats with extra args, and falls back to '[key]'
for missing entries. All panels and init.lua sweep clean of inline
literals — verified by a grep over '"[A-Z][a-z][a-z ]+"'. This sets
up v2's localization-lib-pattern (separate slice, ADR-0036 trigger)
to swap STRINGS without touching the launcher code.

panels/modal.lua

@@ -10,9 +10,9 @@ local FONT_BTN       = 18
 local PADDING        = 18
 
 -- def = {
---   title    = "Confirm",
---   body     = "text or array of lines",
---   buttons  = { { id="cancel", label="Cancel" }, { id="ok", label="Launch anyway", disabled=false } },
+--   title    = <localized-title-string>,
+--   body     = <line-or-array-of-localized-lines>,
+--   buttons  = { { id=<key>, label=<localized-label>, disabled=<bool> }, ... },
 -- }
 function M.render(def, screen_w, screen_h)
     -- Backdrop.