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/theme/plugin.rs

@@ -3,10 +3,8 @@
 //! with the currently-loaded theme so existing card-rendering systems
 //! pick up the new artwork on the next state-changed tick.
 //!
-//! Phase 4 of `CARD_PLAN.md`. The plugin's `set_theme` helper is the
-//! public API that the future picker UI (Phase 6) calls; for now it's
-//! exposed for tests and for any embedder that wants to load an
-//! alternative theme manually.
+//! The plugin's `set_theme` helper is the public API used by the
+//! Settings appearance picker and exposed for tests.
 
 use std::collections::HashMap;