chore: unpin soldr in .clud/settings.json so clud stops downgrading the global soldr

[zackees]

What was wrong

.clud/settings.json pinned "soldr_version": "0.7.11" under optimize.rust. The pin was added on 2026-06-16 (1ec6ecd), when clud optimize wrote its old hardcoded --soldr-version default (zackees/clud#349). Until recently the pin did nothing. zackees/clud 09b4fc0 (clud#1025) changed that: clud now checks an explicit pin on every launch and runs uv tool install --force soldr==0.7.11 whenever the installed version differs. That downgrades the global soldr for anyone with a newer one. On 2026-09-14, the same pin in FastLED/fbuild replaced soldr 0.9.15 with 0.7.11.

Fix

• Remove only the soldr_version key. clud now uses whatever soldr is installed, and installs the latest soldr only when it's missing. install_soldr: true and use_soldr_shims: true stay as they are.
• Add tests/test_clud_settings.py. It loads the JSON and fails if soldr_version appears at any depth, and it also asserts that install and shims stay enabled. It is pure file I/O and spawns no processes.

RED -> GREEN

RED (test added, pin still present):

E       AssertionError: .../.clud/settings.json pins soldr at ['optimize.rust.soldr_version']; clud force-reinstalls that exact version on every launch and downgrades the global soldr. ...
FAILED tests/test_clud_settings.py::test_clud_settings_does_not_pin_soldr_version
========================= 1 failed, 1 passed in 0.04s ==========================

GREEN (key removed):

tests/test_clud_settings.py::test_clud_settings_does_not_pin_soldr_version PASSED [ 50%]
tests/test_clud_settings.py::test_clud_settings_keeps_soldr_install_and_shims_enabled PASSED [100%]
============================== 2 passed in 0.03s ===============================

Both runs used running-process -- python -m pytest tests/test_clud_settings.py -v. On the new file, ruff check passes and ruff format --check reports it already formatted.

FastLED/fbuild has the same pin and is being fixed in a separate PR.

Closes #1212

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https://claude.ai/code/session_01Fg9EZEUZcM8uc6ibJc3WSX