refactor: rename nssa/nssa_core → lee/lee_core

Follow the spel fork's `nssa → lee` refactor (chore/update-lez): the
`#[lez_program]` macro now emits `lee_core::…` paths, so the crate must be
referenced by its real name rather than the `nssa_core` alias.

- Cargo.toml: rename the `nssa_core`/`nssa` dep keys to `lee_core`/`lee` and
  drop the now-redundant `package = "lee_core"`/`package = "lee"` aliases
  (dep name == package name).
- Rust: `nssa_core::` → `lee_core::`, `nssa::` → `lee::` across programs,
  modules, and tools.
- Docs: update the library reference in CLAUDE.md and README.md.

Also drop the dead `NSSA_WALLET_HOME_DIR` env var — superseded by
`LEE_WALLET_HOME_DIR`, which is the only wallet-home var any v0.2.x wallet
reads — from the test tooling (setup-amm-testnet.sh, custom-token.mjs,
run-basecamp-e2e.sh) and docs.

Closes #225

programs/stablecoin/core/src/protocol_parameters.rs

@@ -5,7 +5,7 @@
 //! instruction.
 
 use borsh::{BorshDeserialize, BorshSerialize};
-use nssa_core::{
+use lee_core::{
     account::{AccountId, Data},
     program::{PdaSeed, ProgramId},
 };