refactor: remove deprecated devx.ci.discover_runners wrapper

All workflows now use devx.molecule.discover_runners directly. The
deprecated wrapper (added in Phase 1c for backward compatibility) is
no longer referenced by any workflow in devx, grm, or infra.

- Delete src/devx/ci/discover_runners.py
- Remove `devx ci discover-runners` CLI subcommand
- Update tests to import from devx.molecule.discover_runners
- Remove TestDeprecationWrapper class
- Update docs, README, AGENTS.md, ADR-0002

DEVX-160

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

tests/unit/test_cli.py

@@ -73,13 +73,6 @@ class TestCiCommands:
         assert result.exit_code == 0
         mock_run.assert_called_once_with("devx.ci.detect_release_commit", [])
 
-    @patch("devx.cli._run_module")
-    def test_ci_discover_runners(self, mock_run: MagicMock) -> None:
-        runner = CliRunner()
-        result = runner.invoke(cli, ["ci", "discover-runners", "positional"])
-        assert result.exit_code == 0
-        mock_run.assert_called_once_with("devx.ci.discover_runners", ["positional"])
-
     @patch("devx.cli._run_module")
     def test_ci_doc_coverage(self, mock_run: MagicMock) -> None:
         runner = CliRunner()

tests/unit/test_discover_runners.py

@@ -1,8 +1,6 @@
-"""Unit tests for devx.ci.discover_runners (deprecated wrapper).
+"""Unit tests for devx.molecule.discover_runners.
 
-The wrapper re-exports from devx.molecule.discover_runners; these tests
-verify backward compatibility by importing through the wrapper and
-patching the canonical implementation's requests module.
+Tests verify the canonical implementation by patching the requests module.
 """
 
 import json
@@ -13,7 +11,7 @@ import click
 import pytest
 from click.testing import CliRunner
 
-from devx.ci.discover_runners import (
+from devx.molecule.discover_runners import (
     DEFAULT_MAX_RUNNERS,
     generate_indices,
     get_runner_count,
@@ -266,29 +264,3 @@ class TestMain:
         assert result.output.strip() == "3"
         args, _ = mock_count.call_args
         assert args[1] is None  # token passed as None when missing
-
-
-class TestDeprecationWrapper:
-    def test_re_exports_canonical_symbols(self) -> None:
-        """The wrapper re-exports the canonical implementation's symbols."""
-        from devx.ci import discover_runners as ci_mod
-        from devx.molecule import discover_runners as mol_mod
-
-        assert ci_mod.query_runners is mol_mod.query_runners
-        assert ci_mod.get_runner_count is mol_mod.get_runner_count
-        assert ci_mod.generate_indices is mol_mod.generate_indices
-        assert ci_mod.main is mol_mod.main
-        assert ci_mod.DEFAULT_MAX_RUNNERS is mol_mod.DEFAULT_MAX_RUNNERS
-
-    def test_emit_deprecation_warning(self) -> None:
-        """_emit_deprecation_warning issues a DeprecationWarning."""
-        import warnings
-
-        from devx.ci.discover_runners import _emit_deprecation_warning
-
-        with warnings.catch_warnings(record=True) as caught:
-            warnings.simplefilter("always")
-            _emit_deprecation_warning()
-        assert len(caught) == 1
-        assert issubclass(caught[0].category, DeprecationWarning)
-        assert "deprecated" in str(caught[0].message)