fix(server): allow Bulletin allocation on wasm

[replghost]

Problem

truapi-server compiles Bulletin allowance allocation out on wasm32, returning NativeOnly even when a browser host supplies the canonical People/Bulletin runtime services. This prevents the WASM signing host from proving a lite-person ring and claiming long-term Bulletin storage.

Change

• removes the target-specific allocation stub and compiles the canonical allocator for WASM;
• uses web-time for the WASM wall clock while native hosts retain std::time::SystemTime;
• uses the existing statement-renewal and Bulletin RPC services for claim construction, authorization refresh, and bounded waits;
• records a patch changeset for @parity/truapi-host.

Protocol ownership remains in TrUAPI. Browser hosts only provide the existing chain-service callbacks.

Verification

• cargo +nightly fmt --check
• cargo check --target wasm32-unknown-unknown -p truapi-server --no-default-features --features wasm-signing-host
• cargo test -p truapi-server --all-features: 654 passed
• Merged Epoca integration PR paritytech/epoca#321
• Immutable Epoca Linux build: https://github.com/paritytech/epoca/actions/runs/32172498951
• Live Epoca host-playground: allowance claim passed in 25.3s; preimage lookup in 0.8s; two consecutive signed preimage stores in 9.0s and 6.0s.