Pokemon Silver as a full launcher version, plus launcher mods-list and title-tempo fixes

Silver: derived import manifest (tools/make_silver_manifest.py re-resolves
the Gold manifest's symbols from pokesilver.sym), silver GameVersion row,
generation-keyed extractor routing, required-files override, edition save
stamping (a Silver playthrough no longer writes into the Gold save),
checkver-driven edition data, SILVER/KAMON/OSCAR/MAX presets, GOLD rival
default, edition credits banner, Lugia title screen (OAM layouts, bob,
trail, palettes as title.lua data keys with Gold defaults so old caches
need no re-import), packaging for every build target, docs, and tests.

Launcher: the installed-mods list is one continuous scroll (rows culled to
the viewport) instead of a pager with an inner scroll viewport; the pad
cursor's edge-scroll no longer runs it to the bottom. The game dropdown
shows just the initial and caret. Find-tab behavior unchanged.

Title tempo: a sprite-anim frame shows duration+1 ticks
(engine/sprite_anims/core.asm GetSpriteAnimFrame), which locks both
editions' 64-tick wing beat to the 64-tick sine bob; the title screens no
longer run fast and out of phase.

tests/engine/gate_gen2_mod_api.lua

@@ -23,6 +23,7 @@ T.eq(GameVersion.generation("red"), 1, "Red is Gen 1")
 T.eq(GameVersion.generation("blue"), 1, "Blue is Gen 1")
 T.eq(GameVersion.generation("yellow"), 1, "Yellow is Gen 1")
 T.eq(GameVersion.generation("gold"), 2, "Gold is Gen 2")
+T.eq(GameVersion.generation("silver"), 2, "Silver is Gen 2")
 
 -- ------- 2. manifest: gen2compat is opt-in and defaults off