feat(wasm): add parse_month_year, base32_decode_lenient, guess_mime exports

Plan B Phase 8 — three #[wasm_bindgen] exports for the parsers migrated
in Phase 7, mirrored in extension/src/wasm.d.ts under "Pure parsers
(no session needed)". snake_case JS naming consistent with every
existing export; SessionHandle not required.

- parse_month_year(s) → { month, year } via js_value_for
- base32_decode_lenient(s) → Uint8Array
- guess_mime(filename) → string

Tests in session_tests mod cover the OK paths; error-path / JsValue
serialization can't be tested natively (JsError construction panics
off-wasm) and is covered in core (time::tests + base32::tests).

Plan C will wire SW message handlers consuming these exports in a
future round; this commit delivers only the seam.

Includes simplify-feedback fixes:
- relicario-core lib.rs module-list mentions base32 and mime
- item_types/totp.rs neighbour comment unified to ///-style block

cargo test --workspace: green
cargo clippy --workspace: silent
cargo build -p relicario-wasm --target wasm32-unknown-unknown: clean
cd extension && npm run test: 17 pre-existing failures only (baseline)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

extension/src/wasm.d.ts

@@ -59,6 +59,11 @@ declare module 'relicario-wasm' {
   export function extract_image_secret(image_bytes: Uint8Array): Uint8Array;
   export function embed_image_secret(carrier: Uint8Array, secret: Uint8Array): Uint8Array;
 
+  // Pure parsers (no session needed)
+  export function parse_month_year(s: string): { month: number; year: number };
+  export function base32_decode_lenient(s: string): Uint8Array;
+  export function guess_mime(filename: string): string;
+
   export function totp_compute(config_json: string, now_unix_seconds: bigint): TotpCode;
 
   export function register_device(name: string): {