Pick up engine 0.14.3 — 16k context-window floor and wider compaction margin

[DevMando]

Summary

Picks up engine release 0.14.3 (MandoCode #70). No desktop code changes — this is the submodule pin plus a CHANGELOG entry.

What the engine update brings to the desktop app

• 16k context-window floor. Live testing on a small local model showed the old 8k tier was unusable: the system prompt and tool definitions filled most of the window before any conversation happened, so the model constantly summarized itself and invented details to fill the gaps. The default and the under-7B auto-sizing tier both move to 16k (7B+ stays at 32k). Sub-3B models pay well under 1 GB of extra memory for it.
• Wider compaction safety margin. The "summarize before the window overflows" check now leaves room for a web search's results to land mid-turn, closing the gap where a turn could still die with a "context window filled" error one message before compaction kicked in.

Scope and risk

• Pin bump only; behavior arrives via the engine, covered by its own PR and 505 passing tests.
• Existing agents keep their stored window until their next model switch, which auto-updates it.

Verification

• Desktop builds clean against the pinned engine; 223/223 desktop tests pass (no desktop code touched).