chore: Prep for 1.12.2 Release

[sd-db]

Summary

Release prep for dbt-databricks 1.12.2. Touches only the two release files:

• CHANGELOG.md — set the 1.12.2 heading date to Jul 9, 2026 and finalize the section (conformance cleanup + newly-added entries; see below).
• dbt/adapters/databricks/__version__.py — bump 1.12.1 → 1.12.2.

CHANGELOG changes in this PR

• Add #1508 (Under the Hood): record/replay instrumentation for add_query, get_relation_config, is_uniform, has_dbr_capability, is_cluster (test-only, no runtime impact).
• Consolidate the coverage-run test work into a single Under-the-Hood entry spanning the release's ~38 test/CI PRs, replacing the several partial test lines that were scattered across the section. The #1576 kernel integration-test workflow line is kept separate (tied to the kernel feature).
• Conformance pass per AGENTS.md: fix bare PR links ([1440]/[1467]/[1539] → [#…]), normalize partially solves → partially resolves and closes → resolves on the touched entries.

Test plan

• hatch run code-quality — ruff / ruff format / mypy pass. (uv-lock --check is a known local-config false-negative; this PR does not touch pyproject.toml / uv.lock.)
• hatch run unit — 1258 passed, 6 skipped, 0 failures.
• hatch run pre-commit run --files CHANGELOG.md dbt/adapters/databricks/__version__.py — pass.
• CI (code quality, unit 3.10–3.13, build) to run on this PR.

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
dbt/adapters/databricks
__version__.py
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