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_sync/Cargo.toml

@@ -9,3 +9,6 @@ serde      = { workspace = true }
 uuid       = { workspace = true }
 chrono     = { workspace = true }
 thiserror  = { workspace = true }
+
+[lints]
+workspace = true

solitaire_sync/src/merge.rs

@@ -755,14 +755,14 @@ mod tests {
     fn progress_total_xp_takes_max() {
         let mut local = default_payload();
         local.progress.total_xp = 1500;
-        local.progress.level = crate::progress::level_for_xp(1500);
+        local.progress.level = level_for_xp(1500);
         let mut remote = default_payload();
         remote.progress.total_xp = 2500;
-        remote.progress.level = crate::progress::level_for_xp(2500);
+        remote.progress.level = level_for_xp(2500);
 
         let (merged, _) = merge(&local, &remote);
         assert_eq!(merged.progress.total_xp, 2500);
-        assert_eq!(merged.progress.level, crate::progress::level_for_xp(2500));
+        assert_eq!(merged.progress.level, level_for_xp(2500));
     }
 
     #[test]
@@ -815,7 +815,7 @@ mod tests {
 
         let (merged, _) = merge(&local, &remote);
         assert_eq!(merged.progress.total_xp, 5500);
-        assert_eq!(merged.progress.level, crate::progress::level_for_xp(5500));
+        assert_eq!(merged.progress.level, level_for_xp(5500));
     }
 
     // -----------------------------------------------------------------------
@@ -1051,11 +1051,11 @@ mod tests {
         // drop the oldest 50 so the cap is preserved.
         let start = nd(2024, 1, 1);
         let local_dates: Vec<NaiveDate> = (0..DAILY_CHALLENGE_HISTORY_CAP as i64)
-            .map(|i| start + chrono::Duration::days(i))
+            .map(|i| start + Duration::days(i))
             .collect();
         let remote_dates: Vec<NaiveDate> = (DAILY_CHALLENGE_HISTORY_CAP as i64
             ..DAILY_CHALLENGE_HISTORY_CAP as i64 + 50)
-            .map(|i| start + chrono::Duration::days(i))
+            .map(|i| start + Duration::days(i))
             .collect();
 
         let mut local = default_payload();
@@ -1073,7 +1073,7 @@ mod tests {
         // is therefore start + 50 days.
         assert_eq!(
             merged.progress.daily_challenge_history.first().copied(),
-            Some(start + chrono::Duration::days(50))
+            Some(start + Duration::days(50))
         );
         // Most recent retained is the last remote date.
         assert_eq!(