feat(opencode): add OpenCode plugin support

[growwithsmc]

Summary

Adds Catenary LSP integration for OpenCode via a JavaScript plugin.

Changes

Rust source patches:

• HostFormat::Opencode enum variant in src/cli/mod.rs — maps to --format=opencode CLI flag
• OpenCode payload extractors in src/cli/hooks.rs — reads tool_name, tool_input, cwd, session_id from OpenCode's hook context shape
• format_deny / format_stop_block / format_system_message for OpenCode JSON response shape
• InstallHost::Opencode + run_install_opencode in src/main.rs and src/cli/install.rs — installs plugin to ~/.config/opencode/plugin/catenary.mjs

Plugin (plugins/catenary-opencode/catenary.mjs):

• Hooks: tracks file edits via tool.execute.before, triggers diagnostics via tool.execute.after
• catenary-grep — LSP-powered semantic search
• catenary-glob — filesystem browse with LSP symbol outlines
• catenary-sed — LSP-aware find-and-replace with preview
• catenary-diagnostics — pull diagnostics for all session-tracked files
• catenary-doctor — LSP server health check (works on all platforms including Windows without daemon)

Platform notes

• Unix / WSL with daemon: full LSP features via catenary grep/glob/sed/diagnostics
• Windows without daemon: hook IPC silently degrades; catenary-doctor always works; other tools show helpful fallback messages. Set CATENARY_WSL=true to route through WSL for full features.
• Pre-built Windows binary: compatible — plugin uses --format=claude for hook IPC

Testing

• cargo build --release succeeds on Linux (WSL)
• Plugin syntax validated (node --check)
• catenary doctor works on Windows (pre-built binary)
• All 12 new unit tests pass (cargo test extract_shell_command_opencode*, etc.)

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