fix: Claude multimodal support leaks temporary image files indefinitely

[sam-saffron-jarvis]

What

Track Claude CLI temp image files created from multimodal prompt/tool-result data and remove them when the turn or provider session finishes.

Why

Without cleanup, every uploaded image or tool-result image materialized into /tmp is leaked indefinitely. Repeated multimodal use can eventually exhaust disk space and break later requests.

[SamSaffron]

Closing in favor of consolidated local changeset on branch pr-consolidation. The change from this PR was folded in along with: #387, #389, #390, #391, #400, #401, #402, #403, #404. Build and full test suite pass.