feat(review-action): project_dir input for monorepo dbt projects (avoid the --cwd CLI workaround)

The composite GitHub Action (github/review) assumes the dbt project is at the repo root: it runs 'altimate review' from the job working dir and resolves the manifest relative to it. In a monorepo where the dbt project lives in a subdir (e.g. altimate-ingestion's packages/transform-snowflake/dbt), the action can't be used directly — we had to bypass the composite action and invoke the CLI in a run step with 'altimate review --cwd ' (see AltimateAI/altimate-ingestion #677/#678).

Ask: add a 'project_dir' (a.k.a. working_directory) input to the action that maps to 'altimate review --cwd ', and resolve manifest_path relative to it, so monorepo repos can use the composite action directly. Validated end-to-end that --cwd correlates changed models correctly for a subdir project; this just surfaces it as a first-class action input.