feat: Expand dbt version support (1.7.x - 1.10.x) and fix dbt 1.8+ compatibility

[dgniewek]

Expand dbt version support (1.7.x - 1.10.x) and fix dbt 1.8+ compatibility

Changes

dbt Version Support Expansion

• Expanded all adapter version ranges: >=1.7.x,<2.0.0 (Snowflake, BigQuery, Postgres, Redshift, Glue)
• Removed dbt-core from base requirements (adapters provide it transitively)
• Added Snowflake adapter to test matrix (tox.ini)
• Relaxed Jinja2 constraint: ==3.1.2 → >=3.1.3,<4

dbt 1.8+ Compatibility Fix

• Critical: Refactored publish.py to parse manifest.json as plain JSON instead of using dbt Python API
• Removed imports: dbt.contracts.graph.manifest.Manifest, dbt.contracts.graph.nodes.*
• Added defensive error handling with .get() for missing keys
• Works across dbt 1.7.x through 1.10.x (verified with 70 test executions)

Test Coverage

• Added 17 comprehensive unit tests for manifest parsing:
  • P0 (6 tests): Critical error cases (missing nodes, corrupt JSON, invalid structure)
  • P1 (4 tests): Important scenarios (full metadata, empty columns, multiple models)
  • P2 (7 tests): Edge cases (None values, mixed resource types, empty manifests)
• All tests use plain JSON dicts instead of dbt Python objects

Documentation

• Updated coverage badge (CodeClimate → shields.io, 95%)
• Added troubleshooting section for dbt pre-release edge case
• Created design doc: design/001-dbt-manifest-api-migration.md (complete ADR with test matrix)
• Updated AGENTS.md with dbt 1.8+ fix details and PEP 440 pre-release behavior

Dependency Cleanup

• Removed MarkupSafe pin (managed by Jinja2)
• Removed Werkzeug (unused)
• Fixed GitPython optional import

Breaking Changes

None. Users must continue installing with adapter extras:

pip install data-pipelines-cli[snowflake]  # Required (no change)