new: Add workspace root level setup_environment and install_dependencies actions.

[milesj]

Adds workspace root level setup_environment and install_dependencies support to the action graph, and wires environment setup into moon setup.

Action graph builder

• New install_dependencies_root(spec) and setup_environment_root(spec) methods that are not associated with a project. They locate the dependencies root starting from the workspace root (workspace-level toolchain config only), and only insert actions when the located root is the workspace root — otherwise they insert nothing at all (no SyncWorkspace/SetupToolchain side effects) and return None. Nested dependency roots are expected to be handled by their owning projects.
• Nodes are created with no project_id and an empty root, so they dedupe with project-based installs that resolve to the workspace root.
• Refactored the project-based flows into shared internal_install_dependencies / internal_setup_environment methods, with a shared locate_dependencies_root helper covering both project and workspace starting points.
• The locate helper returns an empty output for toolchains without tier 2 support, so root methods degrade to None instead of failing on a missing plugin function.

Setup command

• moon setup now also sets up each configured toolchain's environment via setup_environment_root, when its dependency root is the workspace root.
• Simplified the summary output.

Tests

• New setup_env, install_deps_root, and setup_env_root test suites for the builder, covering the root-matching gate, deps workspace members, dedupe with the project-based flow, tier gating, and pipeline action switches.

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will regress 2 benchmarks

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 4 improved benchmarks
❌ 2 regressed benchmarks
✅ 17 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	hash_files[1000]	9.8 ms	15 ms	-34.92%
❌	WallTime	load_one	28.3 ms	40.4 ms	-30.02%
⚡	WallTime	build_graphs_async[1000]	128 ms	82.4 ms	+55.26%
⚡	WallTime	build_graphs_async[100]	43 ms	31.6 ms	+36.06%
⚡	WallTime	build_graphs_sync[1000]	507.5 ms	383.5 ms	+32.36%
⚡	WallTime	build_graphs_sync[100]	46 ms	34.9 ms	+31.9%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing 2.5-root-actions (cae91b3) with develop-2.5 (9c3f756)}