Refactor component terminology to programs in config and manifest

- Updated the terminology from "components" to "programs" across the codebase, including in config loading, saving, and manifest specifications.
- Introduced a new `stacks.py` file to handle lifecycle actions for development stacks, implementing handlers for Python and React Vite stacks.
- Adjusted tests to reflect the new program structure and ensure proper functionality.
- Revised documentation to align with the new terminology and structure, ensuring clarity on the purpose and configuration of programs, services, and jobs.

docs/stacks/python-cli.md

@@ -314,7 +314,7 @@ uv run ruff format .        # Format
 ## Registering in castle.yaml
 
 ```yaml
-components:
+programs:
   my-tool:
     description: Does something useful
     source: components/my-tool
@@ -326,7 +326,7 @@ components:
 Tools with system dependencies declare them in the component:
 
 ```yaml
-components:
+programs:
   pdf2md:
     description: Convert PDF files to Markdown
     source: components/pdf2md
@@ -337,7 +337,7 @@ components:
       system_dependencies: [pandoc, poppler-utils]
 ```
 
-Tools live in the `components:` section. If a tool also runs on a schedule,
+Tools live in the `programs:` section. If a tool also runs on a schedule,
 add a separate entry in the `jobs:` section referencing the component.
 
 See @docs/component-registry.md for the full registry reference.

docs/stacks/python-fastapi.md

@@ -99,7 +99,7 @@ settings = Settings()
 Castle passes config via env vars in castle.yaml:
 
 ```yaml
-components:
+programs:
   my-service:
     description: Does something useful
     source: components/my-service

docs/stacks/react-vite.md

@@ -108,12 +108,12 @@ The `build` output is a static SPA in `dist/` — just HTML, JS, and CSS files.
 ## Registering as a castle component
 
 A frontend component has a `build` spec (produces static output). Register it
-in the `components:` section of `castle.yaml`. No `run` block needed if Caddy
+in the `programs:` section of `castle.yaml`. No `run` block needed if Caddy
 handles serving directly from the build output.
 
 ```yaml
 # castle.yaml
-components:
+programs:
   my-frontend:
     description: Web dashboard
     source: components/my-frontend