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>

Cargo.toml

@@ -18,6 +18,21 @@ version = "0.1.0"
 license = "MIT"
 rust-version = "1.95"
 
+# Pedantic correctness lints applied across every member crate via
+# `[lints] workspace = true`. `unsafe_code` is "deny" rather than "forbid"
+# so the three Android JNI FFI modules can opt back in with a scoped
+# `#![allow(unsafe_code)]` — `forbid` cannot be locally overridden, which
+# would break the Android build. Pure crates (core, sync) carry no `unsafe`
+# and so remain effectively forbidden in practice.
+[workspace.lints.rust]
+unsafe_code = "deny"
+single_use_lifetimes = "warn"
+trivial_casts = "warn"
+unused_lifetimes = "warn"
+unused_qualifications = "warn"
+variant_size_differences = "warn"
+unexpected_cfgs = "warn"
+
 [workspace.dependencies]
 serde       = { version = "1", features = ["derive"] }
 serde_json  = "1"