chore: bump version to 0.2.15

[wgqqqqq]

Summary

• bump the BitFun product version from 0.2.14 to 0.2.15
• synchronize Rust, npm, installer, Web UI, mobile web, relay, and MiniApp Market version metadata
• update user-visible fallback/default version values and Cargo.lock workspace package entries
• fix the release-signing fallback so Linux downloads the pinned official minisign 0.12 CLI instead of trying to install the library-only minisign crate
• use Homebrew for the macOS fallback and add an Ubuntu regression check that forces the download path

Verification

• cargo metadata --no-deps --locked --format-version 1
• pnpm run type-check:web
• pnpm --dir src/mobile-web run type-check
• pnpm --dir BitFun-Installer run type-check
• cargo test -p bitfun-services-integrations --features announcement --test announcement_contracts (7 passed)
• pnpm run check:github-config
• bash -n scripts/sign-release-assets.sh
• version metadata consistency check
• git diff --check

Not run

• pnpm --dir src/miniapp-market-web run type-check could not run because that package has no local node_modules; TypeScript reported missing react, vitest, and related type declarations.
• the Linux minisign binary cannot execute on the local macOS host; the new Shell Deploy Scripts CI step downloads, verifies, and executes it on Ubuntu.