Bridge PR: integrate #90 into PR2

[jbjardine]

This bridge PR is the official integration path for @jmcollin78's proposal in aceindy#90 into the PR2 branch that backs aceindy#87.

What this keeps:

• the existing PR2 work from codjardine/pr2-sensors-readonly
• @jmcollin78's migration investigation and commit history from Fix pr2 in #87 aceindy/Duepi_EVO#90
• a normal GitHub review/merge flow instead of a silent local port

What this adjusts on top:

• narrow the migration guard so ConfigFlow-only installs do not try to rewrite an entity already using the stable climate unique ID
• preserve the valid legacy/YAML migration path covered by the smoke migration test
• drop the incidental .devcontainer/configuration.yaml and .vscode/launch.json changes from Fix pr2 in #87 aceindy/Duepi_EVO#90 because they are not required for the fix

Validation done in Docker only:

• pytest tests/test_entity_migration.py -q
• pytest tests/test_readonly_entities.py -q
• pytest tests -q
• WORKSPACE=/Users/jbjardine/cursor/DUEPI_EVO bash scripts/smoke_migration.sh --from-ref v2026.03.02

If this bridge PR is merged into codjardine/pr2-sensors-readonly, PR2 can continue toward main with @jmcollin78's contribution preserved in the history and linked discussion.