chore(agent): modernise base → Ubuntu 24.04 / Python 3.12 / CUDA 12.9

Bump the GPU-agent base image from 12.4.1-cudnn-runtime-ubuntu22.04 (Python 3.10,
CUDA 12.4, early-2024) to 12.9.2-cudnn-runtime-ubuntu24.04:

- Ubuntu 24.04 LTS → Python 3.12 — one modern runtime, no more 3.10.
- CUDA 12.9 + cuDNN 9 — current within the CUDA-12 / cuDNN-9 line that the
  default onnxruntime-gpu wheel AND torch cu124 are built against. NOT CUDA 13:
  ONNX Runtime's CUDA-13 support is still nascent (separate wheels + open
  "Unsupported CUDA version: 13" reports), and torch bundles cu124 anyway. The
  GPU (Ampere/Ada, 12 GB) is fine on either — this is a library-alignment call,
  not a hardware limit.
- PIP_BREAK_SYSTEM_PACKAGES=1: 24.04 marks system Python externally-managed
  (PEP 668); a single-purpose container owns its environment, so global installs
  are fine and simplest.
- agent/ruff.toml pinned to py312 (was py310) so CI lints against the real
  runtime; from __future__ import annotations stays (PEP 649 lazy annotations
  are 3.14, so self-refs still evaluate on 3.12).

CI builds the image but has no GPU — validate on the desktop after pull that it
starts and loads CUDAExecutionProvider (not CPU fallback).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/ruff.toml

@@ -1,7 +1,7 @@
-# The agent runs on the CUDA base image's Python 3.10 — NOT the 3.14 that CI's
-# ci-python image and the repo-root ruff.toml target. Pin the agent to py310 so
-# ruff enforces 3.10 compatibility and never auto-applies a 3.11+/3.14-only fix
-# (e.g. unquoting a self-referential annotation, which PEP 649 makes safe on 3.14
-# but NameErrors on 3.10). Inherit the root lint rules.
+# The agent runs on the CUDA base image's Python 3.12 (Ubuntu 24.04) — NOT the
+# 3.14 that CI's ci-python image and the repo-root ruff.toml target. Pin the
+# agent to py312 so ruff enforces 3.12 compatibility and never auto-applies a
+# 3.14-only fix (e.g. unquoting a self-referential annotation, which PEP 649
+# makes safe on 3.14 but NameErrors on 3.12). Inherit the root lint rules.
 extend = "../ruff.toml"
-target-version = "py310"
+target-version = "py312"