feat(opencode): add request route spans

[kitlangton]

Summary

• add a small request tracing helper for instance HTTP handlers
• wrap the high-volume session/config read routes with top-level route spans like SessionRoutes.get and ConfigRoutes.get
• keep the call site generator-friendly so handlers can yield* services directly while still producing clear HTTP parent spans

Verification

• verified in the current local branch and Motel that route spans like SessionRoutes.get now appear as parents of service spans like Session.get
• confirmed the ported files on this branch are byte-for-byte identical to the locally tested version
• note: fresh worktree tsgo hit the known @tsconfig/bun resolution quirk, so runtime verification was done in the active local branch before porting