feat(bulletin): add boards and player mail for 1.9.0

[ewrogers]

Summary

• Add complete bulletin state tracking for global, guild, trade, world, and player-mail sources.
• Expose active sections, entry lists, opened entries, viewport and navigation state, composers, pending operations, and server results through direct RPC and REST.
• Add CLI and HTTP actions for requesting sources, paging, scrolling, navigation, composition, submission, deletion, highlighting, and dismissal.
• Publish server-confirmed bulletin.submitted, bulletin.deleted, and action-aware bulletin.failed SSE events.
• Document the public API, protocol, state model, client-disassembly findings, and operational constraints.
• Prepare workspace and changelog metadata for 1.9.0.

Validation

• cargo fmt --all
• cargo test --workspace --all-features
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• mdbook build docs
• Native Windows i686 rpc-dll test suite: 237 passed
• Native Windows i686 rpc-dll Clippy with warnings denied
• Live supported-client validation for requested boards and mail, world-board interaction, paging, entry navigation, composition, submission, confirmation, and deletion