fix(cli): discover plugin toolsets before validation

[LeonSGP43]

Summary

• run plugin discovery before HermesCLI validates explicitly requested toolsets
• keep constructor-time validation from warning on plugin-provided toolsets outside the main entrypoint
• add a regression test covering the plugin-toolset discovery path

Fixes #29532

Testing

• uv run --frozen pytest -q -o addopts= tests/cli/test_cli_init.py\n- uv run --frozen ruff check cli.py tests/cli/test_cli_init.py\n- git diff --check

[alt-glitch]

Related to #25714 — similar fix (discover plugins before toolset validation) but that PR bundles an entire code_intel feature with scope creep. This PR is the minimal targeted fix. Also related to closed #15499 (same pattern, different code path).

[teknium1]

Thanks for isolating the constructor-time plugin discovery ordering issue. Current main still validates before discovery at cli.py:3883-3890, while the one-shot path already discovers and re-validates unresolved names at hermes_cli/oneshot.py:65-76.

Problems

• The Fixes #29532 linkage does not match the reported symptom. [Bug]: Getting a weird error since I installed and now it's harassing me in tui about the warning #29532 reports Warning: Unknown toolsets: hermes; current regression coverage treats hermes as an invalid corruption of hermes-cli (tests/hermes_cli/test_toolset_validation.py:83-91). Discovering plugins does not address that configuration value.

Suggested changes

• Retarget the closing linkage to the plugin-toolset warning scenario, or provide a direct reproduction connecting [Bug]: Getting a weird error since I installed and now it's harassing me in tui about the warning #29532 to a plugin-provided hermes toolset.

Automated hermes-sweeper review.