v2.0.1: OpenCode V2 support

Same package now works on both OpenCode V1 and V2.

• V2: plugins: [opencode-parser]
• V1: plugin: [opencode-parser] (needs OpenCode 1.18.29+)
• Deps bundled, so plain install just works
• Save-to-markdown now truly unlimited and lands next to the original file

Thanks to @okhiroyuki for the V2 migration.