docs: restructure into docs/ folder, add roadmap and learning notes

- Move AI_DISCLOSURE, THIRD_PARTY_NOTICES, UPSTREAM_SYNC, ipc.md
  into docs/ (ipc.md renamed to IPC.md for consistency)
- Add docs/ROADMAP.md, docs/CHANGELOG.md, docs/CONTRIBUTORS.md,
  docs/LEARNING-JOURNEY.md
- Update README to reflect the v1.0.0 standalone state, drop the
  development section, refresh the architecture tree, add a
  release-cadence block linking to LEARNING-JOURNEY
- Fix stale ChatTwo/* source paths to HellionChat/* across docs
- Update cross-links in PRIVACY, CONTRIBUTING and .github/* so they
  point at the new docs/ paths

Pure documentation pass, no code changes.

docs/AI_DISCLOSURE.md

@@ -0,0 +1,77 @@
+# AI assistance disclosure
+
+This fork uses AI assistance per the [Dalamud Plugin AI Usage Policy](https://github.com/goatcorp/DalamudPluginsD17/)
+at the **Pair** level.
+
+A note up front: Hellion Chat is currently in a rebuild and adjustment
+phase, and there are no plans to submit it to the Dalamud team for review
+while it stays standalone. If the plugin stays out of the official repo I
+technically wouldn't need to disclose any of this, but I'd rather be
+upfront about how it's built.
+
+Hellion Chat is my entry point into game modding and plugin development. I
+have never written a plugin for a game before. I work alone, so I get help
+where I need it. That's not something I want to hide.
+
+## How I actually work
+
+I plan the architecture, decide what gets built, and own every design
+decision. For each change I:
+
+- Read the code Claude drafts before I integrate it
+- Test with my own tooling and in the running game
+- Read the Dalamud log output to verify behaviour
+- Run security and privacy audits on anything that touches user data
+
+One of the main reasons I use AI is consistency. I want the Hellion code to
+match the style of the upstream Chat 2 codebase and stay readable for
+anyone who opens the repo, not just for me. Claude helps me catch when I'm
+drifting from upstream conventions or writing something that only makes
+sense in my own head.
+
+The balance is shifting toward more hand-written work as I get more
+comfortable with Dalamud and plugin development in general.
+
+## What AI is used for
+
+- API explanations (Dalamud, ImGui, .NET specifics I haven't worked with before)
+- Code drafts that I read, edit, and integrate
+- Pattern suggestions and code review
+- Keeping the style aligned with the upstream Chat 2 codebase
+
+## What AI isn't used for
+
+- **Visual assets.** Logos, icons, banners, and screenshots are human-drawn
+  or taken from the running game.
+- **German translations.** Written by me as a native speaker.
+
+## What's where
+
+Upstream Chat 2 (by Infi & Anna, EUPL-1.2) is the foundation and was not
+produced with AI assistance. Hellion-specific code lives in
+`HellionChat/Privacy/`, `HellionChat/Export/`, `HellionChat/Resources/HellionStrings*`,
+`Ui/SettingsTabs/Privacy.cs`, `Ui/FirstRunWizard.cs`, `Ui/HellionStyle.cs`,
+plus the Migrate3 recovery and plugin layout migration in `MessageStore.cs`
+and `Plugin.cs`. These were developed with Pair-level assistance as
+described above.
+
+## If AI-assisted development is a dealbreaker for you
+
+Fair enough. There are solid alternatives that don't rely on AI in their
+development:
+
+- [Chat 2](https://github.com/Infiziert90/ChatTwo), the original upstream
+  this fork is based on
+- [XIV Instant Messenger](https://github.com/NightmareXIV/XIVInstantMessenger),
+  a different approach to chat in FFXIV
+
+Both are good projects. Use what fits you best.
+
+## Tooling
+
+- Claude (Anthropic) via Claude Code CLI
+- Context7 / Microsoft Learn for current Dalamud and .NET documentation
+
+## Contact
+
+Questions about this disclosure: <https://github.com/JonKazama-Hellion/HellionChat/issues>.