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.

core/src/castle_core/manifest.py

@@ -1,4 +1,4 @@
-"""Castle manifest models — component specs, service specs, job specs."""
+"""Castle manifest models — program specs, service specs, job specs."""
 
 from __future__ import annotations
 
@@ -197,11 +197,11 @@ class DefaultsSpec(BaseModel):
 
 
 # ---------------------
-# Component spec — software identity
+# Program spec — software identity
 # ---------------------
 
 
-class ComponentSpec(BaseModel):
+class ProgramSpec(BaseModel):
     """Software catalog entry — what exists."""
 
     id: str = ""