refactor(Compiler): eliminate Maybe Text indirection in CompilationStrategy

- csWriter now writes files directly (WriterOptions -> Pandoc -> FilePath -> IO (Either DocsterError ()))
- csPostProcess no longer takes text content (String -> IO (Either DocsterError ()))
- Each strategy owns its complete output logic (PDF/HTML/DOCX)
- Remove generateOutputFile (eliminated unused CompilationStrategy parameter)
- Pipeline: generateOutputM >>= processOutput => writeAndProcessOutput (1 step)
- Pandoc 3.7 compatibility: writeDocx returns ByteString instead of ()

.gitignore: exclude stack/cabal config and generated files

.gitignore

@@ -1,6 +1,8 @@
 dist-newstyle
 dist-newstyle
 /.stack-work/
+/.stack-root/
+/.cabal-config/
 *.mmd
 *.png
 *.svg
@@ -10,3 +12,10 @@ dist-newstyle
 dist-newstyle
 output/
 *.log
+cabal.project
+lts-24-34.yaml
+stack-setup-2.yaml
+analytics-charts.md
+architecture-deep-dive.md
+devcontainer.org
+root.json