chore: add pedantic workspace lints (#90)

Add [workspace.lints.rust] and wire each member crate up with
[lints] workspace = true:

  unsafe_code = "deny"        (forbid would break the Android JNI build)
  single_use_lifetimes = "warn"
  trivial_casts = "warn"
  unused_lifetimes = "warn"
  unused_qualifications = "warn"
  variant_size_differences = "warn"
  unexpected_cfgs = "warn"

unsafe_code is "deny" rather than the issue's "forbid" so the three
Android JNI FFI modules (android_keystore, android_clipboard, safe_area)
can opt back in with a scoped #![allow(unsafe_code)] — forbid cannot be
locally overridden. Pure crates carry no unsafe and stay clean.

Clean up the warnings the new lints surface:
- 150ish unused_qualifications removed via `cargo fix` (purely syntactic
  redundant-path-prefix removals).
- table_plugin: the TABLE_COLOUR import was #[cfg(test)]-gated while the
  camera clear-colour used the fully-qualified path; unqualifying it left
  a non-test build with no import. Made the import unconditional instead.
- assets/sources: the `as &[u8]` casts in embed_*_svg! coerce each
  fixed-size &[u8; N] to a uniform slice so the tuples fit the
  &[(&str, &[u8])] arrays — load-bearing, so scoped #[allow(trivial_casts)].

Workspace clippy -D warnings and the full test suite pass. Android build
not compiled here (needs the NDK; built separately per CLAUDE.md §15) —
the deny + scoped-allow keeps the JNI unsafe blocks legal.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

solitaire_engine/src/assets/sources.rs

@@ -115,6 +115,10 @@ macro_rules! embed_classic_svg {
 }
 
 /// Every Dark-theme SVG file bundled into the binary.
+// The `as &[u8]` in `embed_dark_svg!` coerces each fixed-size
+// `&[u8; N]` (N varies per file) to a uniform `&[u8]` so the tuples fit
+// this array type. The cast is load-bearing, not trivial.
+#[allow(trivial_casts)]
 const DARK_THEME_SVGS: &[(&str, &[u8])] = &[
     embed_dark_svg!("back.svg"),
     embed_dark_svg!("clubs_ace.svg"),
@@ -172,6 +176,8 @@ const DARK_THEME_SVGS: &[(&str, &[u8])] = &[
 ];
 
 /// Every Classic-theme SVG file bundled into the binary.
+// See `DARK_THEME_SVGS`: the `as &[u8]` cast is load-bearing.
+#[allow(trivial_casts)]
 const CLASSIC_THEME_SVGS: &[(&str, &[u8])] = &[
     embed_classic_svg!("back.svg"),
     embed_classic_svg!("clubs_ace.svg"),