feat(launcher): launch button + dep-conflict modal

Detail-panel bottom-right Launch button: switches to the selected
module via engine.switch_module if dep-check is clean, otherwise
opens a modal listing conflicts with Cancel + 'Launch anyway'. The
latter is greyed out unless engine.module.switch_module_supports_fallback
is exposed (separate engine slice). FSM adds STATE_MODAL_CONFLICT
with transitions to/from STATE_LIST via cancel/launch_anyway/esc.

Generic panels/modal.lua takes a def-table (title/body/buttons) and
returns the clicked button id from handle_click; reusable for future
modals beyond the conflict case.

init.lua

@@ -15,6 +15,7 @@ end
 local list_panel   = require_panel("list")
 local detail_panel = require_panel("detail")
 local carousel     = require_panel("carousel")
+local modal_panel  = require_panel("modal")
 
 local STATE_LIST, STATE_QUIT, EXIT = fsm.STATE_LIST, fsm.STATE_QUIT_CONFIRM, fsm.EXIT
 local state = STATE_LIST
@@ -339,6 +340,30 @@ function update(ctx, dt)
 
     local mx, my = engine.input.get_mouse_pos()
 
+    -- L.7: Conflict-modal takes priority over STATE_LIST input. esc /
+    -- Cancel close the modal back to STATE_LIST; "Launch anyway" stays
+    -- a no-op until engine.module.switch_module_supports_fallback ships.
+    if ctx_panels.modal_open == "conflict" then
+        if input.was_action_pressed("ui_back") then
+            ctx_panels.modal_open = nil
+            state = fsm.next(state, "esc")
+        elseif input.was_action_pressed("ui_click") then
+            local id = modal_panel.handle_click(ctx_panels.modal_def, mx, my)
+            if id == "cancel" then
+                ctx_panels.modal_open = nil
+                state = fsm.next(state, "cancel")
+            elseif id == "launch_anyway" then
+                local mid = ctx_panels.modal_def.module_id
+                ctx_panels.modal_open = nil
+                state = fsm.next(state, "launch_anyway")
+                if engine.module.switch_module_supports_fallback then
+                    engine.switch_module(mid, { mode = "fallback" })
+                end
+            end
+        end
+        return
+    end
+
     if state == STATE_LIST then
         if input.was_action_pressed("ui_back") then
             state = fsm.next(state, "esc")
@@ -370,6 +395,11 @@ function render(ctx)
     list_panel.render(ctx_panels)
     detail_panel.render(ctx_panels)
 
+    -- L.7: Conflict modal renders above the panels (backdrop dims them).
+    if ctx_panels.modal_open == "conflict" then
+        modal_panel.render(ctx_panels.modal_def, screen_w, screen_h)
+    end
+
     if state == STATE_QUIT then
         engine.render.draw_rect(0, 0, screen_w, screen_h, COLOR_DIM)
         local modal_w, modal_h = 360, 140