fix: batch fixes for issues #2174, 2175, 2176, 2177, 2179, 2196, 2197, 2198, 2199, 2201 [skip ci] (#381)

Fixes:
- #2174: Exit code 0 when response truncated - now exits with code 2 on truncation
- #2175: Conflicting temperature/top-p - warns when both are specified
- #2176: Unknown session fields dropped - uses serde flatten to preserve extra fields
- #2177: DNS cached indefinitely - adds pool_idle_timeout for DNS re-resolution
- #2179: Temperature validation floating-point - uses epsilon-based comparison
- #2196: UTF-8 streaming corruption - adds Utf8StreamBuffer for multi-byte handling
- #2197: --no-session with resume - validates flag incompatibility
- #2198: MCP reconnection fd leak - cleans up before reconnection attempts
- #2199: YAML anchor/alias failures - adds merge key resolution
- #2201: History navigation in tmux - improves bounds checking and docs

Co-authored-by: Bounty Bot <bounty-bot@factory.ai>
Co-authored-by: Droid Agent <droid@factory.ai>

Author: 3 people