Fix dev branch selection: use highest major version, not newest commit date
### Problem/Motivation
Change dev branch selection to prioritize the highest major version instead of the most recently committed branch, preventing the bot from targeting obsolete majors when maintainers backport fixes. Order compatible dev branches by major version, with release-date tie-breaking within a single major. Add web support to the bot path so manual UI runs can drive test-set jobs without posting to production, and reduce CI resources for env-check jobs.
### Work items
- Commit(s): [16b715e2bd](https://git.drupalcode.org/project/project_analysis/-/commit/16b715e2bd6a), [803d6192fb](https://git.drupalcode.org/project/project_analysis/-/commit/803d6192fb4e), [0721aa38bc](https://git.drupalcode.org/project/project_analysis/-/commit/0721aa38bc95)
### Credit
- Implemented by: @bbrala
- Reviewed / helped by: @cmlara
- Test-project feedback: @goba, @nicxvan, @wimleers, @rfay, @larowlan
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*Filed retroactively as part of the Drupal 12 rector coverage effort. Closed as fixed; credit to be applied to the contributors listed above.*
*AI was used extensively to build this work and to file this issue. See [Dries Buytaert: AI-generated Rector rules for Drupal](https://dri.es/ai-generated-rector-rules-for-drupal) and [Björn Brala: Drupal Rector rules are config, not code. Mostly.](https://www.linkedin.com/pulse/drupal-rector-rules-config-code-mostly-bj%C3%B6rn-brala-vfpwe/).*
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