Require explicit CrewAI project definitions (#6358)

* Require explicit CrewAI project definitions

JSON crews and declarative flows now resolve from `[tool.crewai]`
metadata instead of implicit filename discovery. This makes project type
selection deterministic, prevents stray `crew.json(c)` files from changing
CLI behavior, and centralizes definition path validation for run, install,
deploy validation, plotting, and memory reset paths.

`[tool.crewai].definition` must be a project-local file path. Absolute
paths, `~`, missing files, directories, and paths escaping the project root
are rejected so deploy and runtime commands use the same contract.

Breaking changes and migration paths:

* JSON crew projects are no longer discovered from `crew.json` or
  `crew.jsonc` alone. Add explicit metadata:

  ```toml
  [tool.crewai]
  type = "crew"
  definition = "crew.jsonc"
  ```

* Declarative flow projects must use a valid project-local definition path:

  ```toml
  [tool.crewai]
  type = "flow"
  definition = "flows/research.yaml"
  ```

* `Flow.from_definition(definition)` is removed. Use:

  ```python
  Flow.from_declaration(contents=definition)
  ```

* `FlowDefinition.to_json()` and `FlowDefinition.to_yaml()` are removed.
  Use `FlowDefinition.to_dict()` and serialize with the caller's JSON or
  YAML library.

* `FlowDefinition.from_dict()` is removed. Use:

  ```python
  FlowDefinition.from_declaration(contents=data)
  ```

* `FlowDefinition.json_schema()` is removed. Use Pydantic's schema API only
  where schema generation is intentionally needed:

  ```python
  FlowDefinition.model_json_schema(by_alias=True)
  ```

* `crewai_cli.run_crew.find_crew_json_file()` and `_has_json_crew()` are
  removed. Use `configured_project_json_crew()` or the shared
  `crewai_core.project.configured_project_definition("crew")` helper.

* `crewai reset-memories` now only loads JSON crews declared through
  `[tool.crewai].definition`, and invalid declared JSON crew definitions
  fail instead of silently falling back to classic crew discovery.

* Address code review comments

lib/cli/tests/deploy/test_validate.py

@@ -111,7 +111,12 @@ def _run_without_import_check(root: Path) -> DeployValidator:
 
 
 def _scaffold_json_crew(root: Path, *, task_agent: str = "researcher") -> None:
-    (root / "pyproject.toml").write_text(_make_pyproject(name="json_crew"))
+    (root / "pyproject.toml").write_text(
+        _make_pyproject(
+            name="json_crew",
+            extra='[tool.crewai]\ntype = "crew"\ndefinition = "crew.jsonc"',
+        )
+    )
     (root / "uv.lock").write_text("# dummy uv lockfile\n")
     agents_dir = root / "agents"
     agents_dir.mkdir()
@@ -221,7 +226,6 @@ def test_json_crew_reports_project_metadata_before_invalid_json(
     tmp_path: Path,
 ) -> None:
     _scaffold_json_crew(tmp_path)
-    (tmp_path / "pyproject.toml").unlink()
     (tmp_path / "uv.lock").unlink()
     (tmp_path / "crew.jsonc").write_text('{"agents": ["researcher"], "tasks": []}\n')
 
@@ -229,7 +233,6 @@ def test_json_crew_reports_project_metadata_before_invalid_json(
     v.run()
 
     codes = _codes(v)
-    assert "missing_pyproject" in codes
     assert "missing_lockfile" in codes
     assert "invalid_crew_json" in codes
     assert "missing_src_dir" not in codes
@@ -546,17 +549,43 @@ def test_is_json_crew_defers_to_declared_flow_type(tmp_path):
     assert DeployValidator(project_root=tmp_path)._is_json_crew is False
 
 
-def test_is_json_crew_true_for_declared_crew_type(tmp_path):
+def test_is_json_crew_true_for_declared_crew_definition(tmp_path):
+    (tmp_path / "crew.jsonc").write_text("{}")
+    (tmp_path / "pyproject.toml").write_text(
+        '[project]\nname = "demo"\nversion = "0.1.0"\n\n'
+        '[tool.crewai]\ntype = "crew"\ndefinition = "crew.jsonc"\n'
+    )
+
+    assert DeployValidator(project_root=tmp_path)._is_json_crew is True
+
+
+def test_is_json_crew_false_for_declared_crew_without_definition(tmp_path):
     (tmp_path / "crew.jsonc").write_text("{}")
     (tmp_path / "pyproject.toml").write_text(
         '[project]\nname = "demo"\nversion = "0.1.0"\n\n'
         '[tool.crewai]\ntype = "crew"\n'
     )
 
-    assert DeployValidator(project_root=tmp_path)._is_json_crew is True
+    assert DeployValidator(project_root=tmp_path)._is_json_crew is False
 
 
-def test_is_json_crew_true_without_pyproject(tmp_path):
+def test_json_crew_non_string_definition_reports_invalid_definition(
+    tmp_path: Path,
+) -> None:
+    (tmp_path / "pyproject.toml").write_text(
+        '[project]\nname = "demo"\nversion = "0.1.0"\n\n'
+        '[tool.crewai]\ntype = "crew"\ndefinition = ["crew.jsonc"]\n'
+    )
+
+    v = DeployValidator(project_root=tmp_path)
+    v.run()
+
+    finding = next(r for r in v.results if r.code == "invalid_crew_definition")
+    assert finding.severity is Severity.ERROR
+    assert "must be a string" in finding.detail
+
+
+def test_is_json_crew_false_without_pyproject(tmp_path):
     (tmp_path / "crew.jsonc").write_text("{}")
 
-    assert DeployValidator(project_root=tmp_path)._is_json_crew is True
+    assert DeployValidator(project_root=tmp_path)._is_json_crew is False