Epic: Rich Content Support

[bug-ops]

Summary

Currently only ContentBlock::Text is extracted from prompts. Images, embedded resources, resource links, thinking content, and tool call locations are not supported.

Critical Path

[Epics 1+2 complete] ──→ [4.1 Multi-modal prompts]  ─┐
                     ──→ [4.2 Tool locations]         ├ (all parallel)
                     ──→ [4.3 Thinking chunks]        ─┘

• Depends on: Epics 1+2 (Epic: Wire AcpContext into Agent Loop #777, Epic: Session Lifecycle Management #778)
• Parallel with: Epics 3, 5
• All sub-issues are independent

Acceptance Criteria

• Image content in prompts forwarded to LLM
• Embedded resources extracted and inlined
• Tool output includes file locations for IDE navigation
• LLM thinking tokens streamed as AgentThoughtChunk