fix(console): preserve literal SQL in GitHub plan diffs

[Vamsi-klu]

Description

Fixes #5287.

Preserve literal SQL in GitHub plan-summary diffs, including T-SQL bracketed identifiers that Rich currently interprets as markup. A shared Markdown diff emitter captures the original text, prints it literally, and selects a fence longer than any embedded backtick sequence. It covers both model-diff emitters and environment SQL statements.

Regression coverage includes actual T-SQL models, tabs, long lines, markup-like literals, embedded fences, capture ordering, and the mocked final GitHub summary boundary.

Suggested reviewers: erindru, treysp.

Test Plan

• python -m pytest tests/core/test_console.py tests/integrations/github/cicd/test_github_controller.py -q -n 0 -p no:rerunfailures: 63 passed.
• python -m pytest tests/integrations/github/cicd/test_integration.py -k test_merge_pr_has_non_breaking_change -q -n 0 -p no:rerunfailures: 3 passed.
• Reverting the production fix reproduces the regression failures; restoring it passes.
• make style and make fast-test passed on this branch.

Checklist

• I have run make style and fixed any issues
• I have added tests for my changes (if applicable)
• All existing tests pass (make fast-test)
• My commits are signed off (git commit -s) per the DCO