chore(package): migrate to src/ layout

Moved package code from llama_stack/ to src/llama_stack/ following Python
packaging best practices. Updated pyproject.toml, MANIFEST.in, and tool
configurations accordingly.

Public API and import paths remain unchanged. Developers will need to
reinstall in editable mode after pulling this change.

Also updated paths in pre-commit config, scripts, and GitHub workflows.

.pre-commit-config.yaml

@@ -42,7 +42,7 @@ repos:
     hooks:
     -   id: ruff
         args: [ --fix ]
-        exclude: ^llama_stack/strong_typing/.*$
+        exclude: ^src/llama_stack/strong_typing/.*$
     -   id: ruff-format
 
 -   repo: https://github.com/adamchainz/blacken-docs
@@ -86,7 +86,7 @@ repos:
         language: python
         pass_filenames: false
         require_serial: true
-        files: ^llama_stack/distributions/.*$|^llama_stack/providers/.*/inference/.*/models\.py$
+        files: ^src/llama_stack/distributions/.*$|^src/llama_stack/providers/.*/inference/.*/models\.py$
       - id: provider-codegen
         name: Provider Codegen
         additional_dependencies:
@@ -95,7 +95,7 @@ repos:
         language: python
         pass_filenames: false
         require_serial: true
-        files: ^llama_stack/providers/.*$
+        files: ^src/llama_stack/providers/.*$
       - id: openapi-codegen
         name: API Spec Codegen
         additional_dependencies:
@@ -104,7 +104,7 @@ repos:
         language: python
         pass_filenames: false
         require_serial: true
-        files: ^llama_stack/apis/|^docs/openapi_generator/
+        files: ^src/llama_stack/apis/|^docs/openapi_generator/
       - id: check-workflows-use-hashes
         name: Check GitHub Actions use SHA-pinned actions
         entry: ./scripts/check-workflows-use-hashes.sh
@@ -120,7 +120,7 @@ repos:
         pass_filenames: false
         require_serial: true
         always_run: true
-        files: ^llama_stack/.*$
+        files: ^src/llama_stack/.*$
       - id: forbid-pytest-asyncio
         name: Block @pytest.mark.asyncio and @pytest_asyncio.fixture
         entry: bash
@@ -150,7 +150,7 @@ repos:
         name: Format & Lint UI
         entry: bash ./scripts/run-ui-linter.sh
         language: system
-        files: ^llama_stack/ui/.*\.(ts|tsx)$
+        files: ^src/llama_stack/ui/.*\.(ts|tsx)$
         pass_filenames: false
         require_serial: true