feat(04-02): add script download API endpoints and router registration

- imptune/api/scripts.py: GET /printers/{id}/scripts/{install,uninstall,detect}
- 404 for missing printer, 422 for missing driver/INF/driver_desc
- Content-Disposition attachment header on all responses
- imptune/main.py: register scripts.router
- 5 integration tests covering all endpoint cases (200/404/422)

imptune/api/scripts.py

@@ -0,0 +1,94 @@
+"""Script download endpoints — generates and serves PowerShell scripts for a printer."""
+import json
+
+from fastapi import APIRouter
+from fastapi.responses import PlainTextResponse
+
+from imptune.db.models import Printer
+from imptune.generators.script_generator import render_detect, render_install, render_uninstall
+
+router = APIRouter(prefix="/printers")
+
+
+def _get_printer_and_driver(printer_id: int):
+    """Fetch printer and validate driver — returns (printer, driver_name) or PlainTextResponse error."""
+    printer = Printer.get_or_none(Printer.id == printer_id)
+    if printer is None:
+        return None, PlainTextResponse("Printer not found", status_code=404)
+
+    driver = printer.driver
+    if driver is None:
+        return None, PlainTextResponse("No driver assigned", status_code=422)
+
+    if not driver.inf_filename:
+        return None, PlainTextResponse("Driver has no INF file", status_code=422)
+
+    if not driver.driver_desc:
+        return None, PlainTextResponse("Driver has no description", status_code=422)
+
+    try:
+        desc_list = json.loads(driver.driver_desc)
+        driver_name = desc_list[0]
+    except (json.JSONDecodeError, IndexError, TypeError):
+        return None, PlainTextResponse("Driver description is invalid", status_code=422)
+
+    return (printer, driver, driver_name), None
+
+
+@router.get("/{printer_id}/scripts/install")
+def get_install_script(printer_id: int):
+    """Download the PowerShell install script for a printer."""
+    result, error = _get_printer_and_driver(printer_id)
+    if error is not None:
+        return error
+
+    printer, driver, driver_name = result
+    rendered = render_install(
+        printer_name=printer.name,
+        ip_address=printer.ip_address,
+        port_name=printer.port_name,
+        driver_name=driver_name,
+        inf_filename=driver.inf_filename,
+        duplex_mode=printer.duplex_mode,
+        color_mode=printer.color_mode,
+        paper_size=printer.paper_size,
+        collate=printer.collate,
+    )
+    return PlainTextResponse(
+        content=rendered,
+        headers={"Content-Disposition": 'attachment; filename="install.ps1"'},
+    )
+
+
+@router.get("/{printer_id}/scripts/uninstall")
+def get_uninstall_script(printer_id: int):
+    """Download the PowerShell uninstall script for a printer."""
+    result, error = _get_printer_and_driver(printer_id)
+    if error is not None:
+        return error
+
+    printer, driver, driver_name = result
+    rendered = render_uninstall(
+        printer_name=printer.name,
+        driver_name=driver_name,
+        port_name=printer.port_name,
+    )
+    return PlainTextResponse(
+        content=rendered,
+        headers={"Content-Disposition": 'attachment; filename="uninstall.ps1"'},
+    )
+
+
+@router.get("/{printer_id}/scripts/detect")
+def get_detect_script(printer_id: int):
+    """Download the PowerShell detection script for a printer."""
+    result, error = _get_printer_and_driver(printer_id)
+    if error is not None:
+        return error
+
+    printer, driver, driver_name = result
+    rendered = render_detect(printer_name=printer.name)
+    return PlainTextResponse(
+        content=rendered,
+        headers={"Content-Disposition": 'attachment; filename="detect.ps1"'},
+    )