fix(android): A2/A3/A4 — APK build doc, dead refs, modal hit targets

A2: docs/ANDROID.md — remove stale "permanent fix to come" note;
    clarify --lib is the canonical command; root-cause the upstream
    cargo-apk bug. SESSION_HANDOFF.md closes the open item.

A3: Remove dead CARD_PLAN.md references from four source module
    doc comments (theme/importer.rs, theme/plugin.rs, assets/mod.rs,
    assets/svg_loader.rs). Also fix stale "future picker UI" language
    in plugin.rs (picker shipped in Phase 7).

A4: ui_modal.rs spawn_modal_button — add min_height: Val::Px(48.0)
    so every modal action button meets Material's 48 dp touch target
    minimum. Modal button height was 42 px (2×SPACE_3 + TYPE_BODY_LG);
    now clamped to 48 px minimum. Cards at 40 dp on 360 dp phones are
    layout-constrained (7 columns) and cannot be widened.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

solitaire_engine/src/assets/mod.rs

@@ -1,10 +1,8 @@
 //! Asset-loading infrastructure for runtime SVG rasterisation and the
 //! per-platform user-themes directory.
 //!
-//! See `CARD_PLAN.md` for the full multi-phase implementation plan.
-//! This module is the entry point for Phases 1 (SVG → `Image`) and 5
-//! (user-themes directory). Phase 3 will extend it further with custom
-//! `AssetSource` implementations for `embedded://` and `themes://`.
+//! Provides the SVG → `Image` loader and the `embedded://` / `themes://`
+//! custom `AssetSource` implementations used by the theme system.
 
 pub mod card_face_svg;
 pub mod icon_svg;