fix(opencode): honor cli runtime for command routing

[snvtac]

Summary

• route OpenCode runtime selection through a shared helper so runtime: "cli" is an explicit first-class CLI path
• avoid reading bundled HTML for CLI submit_plan, keeping source checkouts and CLI-only workflows independent of embedded assets
• add OpenCode plugin hook coverage for /plannotator-last, /plannotator-annotate, /plannotator-review, and CLI submit_plan without bundled HTML

Issue

Fixes #947

Verification

• bun test apps/opencode-plugin/*.test.ts
• PATH="$PWD/apps/hook/node_modules/.bin:$PWD/packages/ui/node_modules/.bin:$PATH" BUN_INSTALL_CACHE_DIR="$PWD/../bun-cache" bun run typecheck
• bun test
• git diff --check
• bun build embedded.ts --outfile dist/embedded.js --target bun --external @opencode-ai/plugin && bun build index.ts --outfile dist/index.js --target node (run from apps/opencode-plugin with the system Bun binary)

[backnotprop]

Closing this. #947 wasn't a routing bug, it was a frontend crash (same as #949), already fixed in 0.21.1. The runtime change doesn't touch it. Both paths served the same broken page.

Also, runtime: "cli" is a debug switch, not something users should set. Happy to take the resolveRuntimeExecutionMode cleanup as its own refactor if you want. Thanks.