refactor(app): support only v2 servers

[Brendonovich]

Summary

• remove App V1 protocol detection, compatibility routing, and the direct @opencode-ai/sdk dependency
• route App server traffic and event handling through the V2 client only
• own the remaining rendering projection types inside App and migrate fixtures to V2 API shapes
• disable unsupported controls with explicit TODOs until corresponding V2 APIs exist

Validation

• bun typecheck
• bun run typecheck:e2e
• relevant unit tests: 75 passed, 13 V1-only tests skipped
• browser tests: 33 passed
• benchmark unit tests: 43 passed before and after
• bun run build

The full unit suite has one pre-existing Arabic i18n parity failure for five missing translations. Production benchmark screenshot capture remains blocked before launch by the existing Node ESM bun: protocol loader error, so no before/after images are attached.

[Brendonovich]

Superseded by the reviewable V2 stack:

1. test(app): migrate e2e fixtures to v2 #40374 test(app): migrate e2e fixtures to v2
2. refactor(app): own rendering contracts #40375 refactor(app): own rendering contracts
3. fix(app): reconcile v2 session projections #40376 fix(app): reconcile v2 session projections
4. refactor(app): migrate supported v2 APIs #40378 refactor(app): migrate supported v2 APIs
5. refactor(app): gate unsupported v2 capabilities #40381 refactor(app): gate unsupported v2 capabilities
6. refactor(app): remove v1 compatibility #40382 refactor(app): remove v1 compatibility

Each PR is based on the preceding branch.