Correct sdp-expectation-notifications docs: drop coverage, alert naming, destination semantics

[vmariiechko]

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Summary

Documentation-only pass on the sdp-expectation-notifications asset: seven corrections grounded in two live verification sessions (2026-07-26 drop/destination testing, 2026-07-17/18 hygiene build). No pipeline code, YAML defaults, or test behavior changed. Also includes two small ROADMAP.md cleanups and finalizes v1.12.1.

Changes

• Drop coverage documented. The hook filters purely on failed_records > 0 and never inspects the expectation's action type, so warn and drop rules notify identically; the README previously framed the pattern as WARN-only. Adds the lived 2026-07-26 numbers (drop expectation matching the WARN row's shape, dropped_records field, additive backstop sum).
• Naming corrected. "Alert v2"/"Alerts v2" renamed to "Databricks SQL alert(s)" across the README, in-bundle doc, skill files, alert YAML comments, and install prompt text, matching current Databricks docs. alerts-v2 kept only where it names an actual CLI command.
• Notification destinations clarified. Destinations serve only Databricks SQL and jobs, not the event hook, and a destination is a wrapper around a webhook (its own admin setup, Slack/Teams-specific), not a substitute for one. Documents the measured non-deduplication when a destination and user_email share an address.
• No-webhook guidance added. Readers and the companion skill are now steered to deploy the backstop alone when there is no Slack/Teams/webhook target.
• Backstop cron tied to pipeline mode. Flags that a continuous pipeline needs a tighter cron/window than the shipped daily default, at the cost of more warehouse wake-ups.
• Grace-period claim softened. Replaces the overclaimed "roughly 20 seconds" with an honest, unestablished bound and the actionable rule (single-digit-second hook work).
• Skill CLI gotcha documented. databricks notification-destinations create's misleading warning/empty echo, so an agent scripting it doesn't mistake success for failure.
• ROADMAP.md cleanup (unrelated to the asset, bundled here): fills in the placeholder "Pre-commit Hooks" idea with a proper scoped proposal, and adds a new "Shared Bundles Support" idea.

Change Area

• Core template (template/, schema, helpers)
• Asset Library (assets/<name>/)
• Both
• Docs / tests / infrastructure only

Configuration Axes Affected

• Environment setup (full/minimal, dev environment)
• Compute type (classic/serverless/both)
• Permissions / RBAC
• CI/CD pipelines (Azure DevOps, GitHub Actions, GitLab)
• Cloud provider (Azure/AWS/GCP)
• Unity Catalog / schemas
• Template schema (databricks_template_schema.json)
• Template helpers (library/helpers.tmpl)
• Asset Library (new asset, asset schema, or framework changes)
• None of the above (docs, tests, infrastructure only)

Testing

• All tests pass (pytest tests/ -V) — 2446 passed, 163 skipped, unchanged from the pre-edit baseline
• Manual template generation tested
• New tests added for new functionality (docs-only change; no new tests needed, confirmed no existing test asserts the prose being changed)

Release (if this PR cuts a release)

• CHANGELOG.md finalized: [Unreleased] renamed to [1.12.1] - 2026-07-26, fresh empty [Unreleased] added above
• Both version markers bumped to 1.12.1 (pyproject.toml and template/{{.project_name}}/bundle_init_config.json.tmpl)
• Version guard test passes (tests/test_release_metadata.py)

Checklist

• Go template syntax is valid (no unclosed {{ }} blocks)
• No .tmpl files appear in generated output
• Generated YAML files are valid
• Documentation updated (if behavior changed) — N/A, no behavior changed