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.

.github/workflows/providers-list-deps.yml

@@ -7,22 +7,22 @@ on:
     branches:
       - main
     paths:
-      - 'llama_stack/cli/stack/list_deps.py'
-      - 'llama_stack/cli/stack/_list_deps.py'
-      - 'llama_stack/core/build.*'
-      - 'llama_stack/core/*.sh'
+      - 'src/llama_stack/cli/stack/list_deps.py'
+      - 'src/llama_stack/cli/stack/_list_deps.py'
+      - 'src/llama_stack/core/build.*'
+      - 'src/llama_stack/core/*.sh'
       - '.github/workflows/providers-list-deps.yml'
-      - 'llama_stack/templates/**'
+      - 'src/llama_stack/templates/**'
       - 'pyproject.toml'
 
   pull_request:
     paths:
-      - 'llama_stack/cli/stack/list_deps.py'
-      - 'llama_stack/cli/stack/_list_deps.py'
-      - 'llama_stack/core/build.*'
-      - 'llama_stack/core/*.sh'
+      - 'src/llama_stack/cli/stack/list_deps.py'
+      - 'src/llama_stack/cli/stack/_list_deps.py'
+      - 'src/llama_stack/core/build.*'
+      - 'src/llama_stack/core/*.sh'
       - '.github/workflows/providers-list-deps.yml'
-      - 'llama_stack/templates/**'
+      - 'src/llama_stack/templates/**'
       - 'pyproject.toml'
 
 concurrency:
@@ -41,7 +41,7 @@ jobs:
       - name: Generate Distribution List
         id: set-matrix
         run: |
-          distros=$(ls llama_stack/distributions/*/*build.yaml | awk -F'/' '{print $(NF-1)}' | jq -R -s -c 'split("\n")[:-1]')
+          distros=$(ls src/llama_stack/distributions/*/*build.yaml | awk -F'/' '{print $(NF-1)}' | jq -R -s -c 'split("\n")[:-1]')
           echo "distros=$distros" >> "$GITHUB_OUTPUT"
 
   list-deps:
@@ -102,4 +102,4 @@ jobs:
           USE_COPY_NOT_MOUNT: "true"
           LLAMA_STACK_DIR: "."
         run: |
-          uv run llama stack list-deps llama_stack/distributions/ci-tests/build.yaml
+          uv run llama stack list-deps src/llama_stack/distributions/ci-tests/build.yaml