feat(ol-dbt-cli): add SQL/YAML linting and column-level impact analysis CLI

Adds a new `ol-dbt` CLI package at `src/ol_dbt_cli/` with two commands:

## `ol-dbt validate`

Structural consistency checks for dbt models:

1. **YAML/SQL sync** — warns when columns declared in a model's YAML schema
   are absent from its compiled SELECT output, or vice-versa.
2. **Missing upstream refs** — flags `ref()` or `source()` calls that
   resolve to models/sources not present in the project.
3. **Upstream column existence** — validates that columns referenced from
   an upstream model actually exist in that model's output.
4. **Duplicate column aliases** — detects accidental repeated alias names
   within a single model.
5. **SELECT \*** — INFO-level notice for unresolved star expansions;
   `--warn-select-star` promotes these to warnings.

Options:
- `--model/-m` (repeatable): filter to one or more model names, comma-separated
  lists, or directory paths under `models/`
- `--errors-only`: suppress INFO/WARN output, show only errors
- `--warn-select-star`: treat unresolved SELECT * as warnings
- `--compiled-dir`: point at `target/compiled/` for Jinja-heavy models
- `--output json`: machine-readable output

## `ol-dbt impact`

Column-level downstream impact analysis driven by git diffs:

- Reads `git diff [--cached] [base]` to find changed/removed SQL column aliases
- Traverses the manifest or parsed SQL to find all downstream models that
  reference each changed column
- Reports broken references, risky usages, and models needing review

## Jinja pre-processing

Robust regex-based Jinja stripping so sqlglot can parse the raw `.sql` files
without a running dbt environment:

- `{{ ref() }}` / `{{ source() }}` → stable SQL identifiers with reverse maps
- `{{ var() }}` and bare `{{ variable }}` → unquoted placeholders (avoids
  the `''__jinja__''` doubled-quote bug when templates surround with SQL quotes)
- Block-level macro calls alone on a line → SQL comment
- Broken column expressions where a macro splits a SQL column boundary
  (e.g. `{{ array_join('partial SQL', "path") }}`) → collapsed to
  `__jinja__ as alias` via `_BROKEN_COL_RE` cleanup pass

Result: **588/588** dbt models in this project parse successfully.

## YAML registry improvements

- Parses both `models:` and `sources:` blocks for SELECT * resolution
- Rescues model definitions accidentally nested inside another model's
  `columns:` list (YAML authoring error in `_stg_mitlearn_models.yml`)
- Filters out nested-model entries from the parent model's column list

## Tests

85 pytest tests covering all commands, lib modules, and edge cases.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: blarghmatey

pyproject.toml

@@ -15,13 +15,15 @@ dependencies = [
     "cyclopts~=4.8.0",
     "dbt-duckdb>=1.10.0",
     "dbt-trino>=1.10.0",
+    "rich>=13.0",
+    "sqlglot>=25.0",
     "trino[external-authentication-token-cache]>=0.336.0",
     "universal-pathlib ~=0.3.1",
 ]
 repository = "https://github.com/mitodl/ol-data-platform"
 
 [tool.uv.workspace]
-members = ["packages/*"]
+members = ["packages/*", "src/ol_dbt_cli"]
 
 [tool.uv]
 package = false  # This is a workspace root, not a package

src/ol_dbt_cli/ol_dbt_cli/__init__.py

@@ -0,0 +1,55 @@
+"""Main CLI entry point for ol-dbt tooling."""
+
+import sys
+
+import cyclopts
+
+from ol_dbt_cli.commands.impact import impact
+from ol_dbt_cli.commands.validate import validate
+
+app = cyclopts.App(
+    name="ol-dbt",
+    help="""
+    ol-dbt: dbt project analysis and validation CLI
+
+    Tools for the engineering team to reason about in-progress dbt changes,
+    validate model quality, and understand column-level impact.
+
+    Common workflows:
+
+      1. Check what breaks before opening a PR:
+         $ ol-dbt impact --changed-only
+
+      2. Validate model SQL/YAML consistency:
+         $ ol-dbt validate --changed-only
+
+      3. Full validation of all models:
+         $ ol-dbt validate
+
+      4. JSON output for CI pipelines:
+         $ ol-dbt impact --format json
+         $ ol-dbt validate --format json
+
+    Use --help on any command for detailed usage.
+    """,
+    version="0.1.0",
+)
+
+app.command(impact, name="impact")
+app.command(validate, name="validate")
+
+
+def main() -> None:
+    """CLI entry point."""
+    try:
+        app()
+    except KeyboardInterrupt:
+        print("\n\nOperation cancelled by user.", file=sys.stderr)
+        sys.exit(130)
+    except Exception as e:
+        print(f"\nError: {e}", file=sys.stderr)
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()