refactor: move olliesrv and toolsrv packages to cmd/*/internal/
Move server-only packages under their respective cmd directories:
olliesrv:
- agent/ -> cmd/olliesrv/internal/agent/
- backend/ -> cmd/olliesrv/internal/backend/
- bypass/ -> cmd/olliesrv/internal/bypass/
- fs/ -> cmd/olliesrv/internal/fs/
- prompts/ -> cmd/olliesrv/internal/prompts/
- session/ -> cmd/olliesrv/internal/session/
toolsrv:
- Server-only code (exec9p, fs9p, server9p, spec9p, auth9p) -> cmd/toolsrv/
- sandbox/ -> cmd/toolsrv/internal/sandbox/
- Keep shared client code (client9p, spawn, registry, meta) in toolsrv/
- Add toolsrv/types.go for shared types (ToolResult, ToolResultContent)
This enforces package boundaries - code in cmd/*/internal/ cannot be
imported by external packages, while shared code remains importable.
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