Add AI assistant drawer for build analysis

[wangdong3213]

Summary

Adds an optional OpenAI-compatible AI assistant drawer to the build editor. The drawer appears on the right side of an open build, can be collapsed, and provides build analysis or follow-up answers without modifying the build.

What Changed

• Added a right-side AIChatPanel for build analysis chat.
• Added local-only AI settings stored in AIAssistantSettings.json under the user data path.
• Added a minimal non-streaming OpenAI-compatible chat completions client.
• Added an English build snapshot generator covering character info, active sets, skill groups, key stats, items, and warnings.
• Integrated the drawer into Build.lua with small lifecycle insertions while preserving existing tabs, including Compare.

Notes

• This is English-only and does not depend on PoeCharm2 or localization files.
• The assistant gives advice only; it does not write to build XML or change passives, gear, skills, or config.
• API keys are stored locally only and are not included in exported/shared builds.
• Streaming/realtime reasoning display is intentionally out of scope.

Validation

• rg check confirmed no PoeCharm2 or Chinese UI/prompt strings remain in the new AI code.
• git diff --check
• Windows headless startup via runtime/Path{space}of{space}Building-PoE2.exe src/HeadlessWrapper.lua
• Targeted module load check for AI/ProviderPresets, AI/Settings, AI/AIClient, AI/BuildSnapshot, and Classes/AIChatPanel

Local Docker/LuaJIT were not installed, so the full Busted workflow was left to GitHub CI.

[LocalIdentity]

We are not interested in adding AI assistants into Path of Building as we do not believe to be healthy for users and for the game