feat: Interactive Environment Hydration View in TUI

[drlucaa]

Currently, same performs environment hydration (Nix resolutions and builds) in the background or within a generic "Hydrating Environments" span. This obscures critical information like download progress, build logs, and resolution details.

We want to promote the hydration phase to a first-class view in the TUI. Before the main build plan is shown, users should see a list of unique environments being prepared. This view should be interactive, allowing users to "drill down" into specific environments to view real-time, colored logs (preserving Nix progress bars via PTY).

Goals

1. Visibility: Explicitly show the unique environments required for the run (e.g., go@1.25.4, lint@2.7.2) before task execution starts.
2. Rich Feedback: Stream nix print-dev-env output using a Pseudo-Terminal (PTY) to preserve ANSI colors and download progress bars.
3. Consistency: Ensure the interaction model (navigation, drill-down, log inspection) mirrors the existing Task Graph view.

Acceptance Criteria

• Scheduler & Flow

• Scheduler.Run is refactored to calculate unique EnvIDs and call EmitHydration before EmitPlan.

• The execution flow strictly follows: Emit Hydration Plan Hydrate (Parallel) Emit Build Plan Execute Tasks.

• Telemetry

• Tracer interface updated with EmitHydration.

• New MsgInitHydration message implemented to carry environment metadata to the TUI.

• TUI Adapter

• New ViewModeHydration implemented.

• Renders a flat, selectable list of environments using TaskNode styles (Status Icon, Name, Duration).

• Interaction: Users can navigate with j/k and press Enter to view full-screen logs (utilizing Vterm).

• Transition: TUI automatically switches to the Task Graph view (ViewModeTree) when hydration completes.

• Nix Adapter (PTY Support)

• EnvFactory uses creack/pty to execute the "visual" nix print-dev-env command, streaming ptmx output directly to the Span.

• A secondary execution captures the JSON data reliably for environment parsing.