docs: add missing AGENTS.md (and README where missing)

AGENTS.md

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+# AGENTS.md
+
+Cody for Visual Studio — a Windows-only Visual Studio extension (.NET Framework 4.7.2) that
+bundles a Node.js-based Cody agent. C# code lives in `src/`; the agent build scripts live in
+`agent/`. See `CONTRIBUTING.md` for the full development setup.
+
+## Layout
+
+- `src/Cody.sln` — main solution.
+- `src/Cody.Core/` — core library shared across the extension.
+- `src/Cody.UI/` — UI components.
+- `src/Cody.VisualStudio/` — the Visual Studio extension (VSIX) entry point.
+- `src/Cody.VisualStudio.Completions/` — autocomplete component (built separately, see `src/build.ps1`).
+- `src/Cody.Core.Tests/`, `src/Cody.VisualStudio.Tests/` — test projects.
+- `agent/` — PowerShell scripts and version pin (`agent.version`) for building the Node.js agent.
+
+## Setup
+
+Requires Windows, Visual Studio (Pro), the .NET SDK, .NET Framework 4.7.2, Node.js, and
+`pnpm` (the repo pins `8.6.7`). Configure Git with `git config core.autocrlf false` — the repo
+uses Windows line endings.
+
+## Build
+
+The agent must be built before building or debugging the extension for the first time.
+
+```powershell
+# Build the Node.js agent (run from the agent/ directory or with the relative path below)
+./agent/runBuildAgent.ps1
+
+# Build the extension (configuration defaults to Debug)
+./src/build.ps1 -configuration Debug
+```
+
+You can also open `src/Cody.sln` in Visual Studio and press `F5` to build and debug.
+
+## Test
+
+```powershell
+# Run tests against the built test assemblies (matches CI)
+dotnet test src/*Tests/bin/Debug/*.Tests.dll --logger:trx --verbosity detailed
+```
+
+Integration/UI tests can also be run from Visual Studio's Test Explorer (right-click
+`Cody.VisualStudio.Tests` → Run). UI tests require an access token; see `CONTRIBUTING.md`.
+
+## Lint / Format
+
+CI enforces formatting with `dotnet format`. Verify locally before committing:
+
+```powershell
+dotnet format ./src/ --verify-no-changes -v:diag
+```
+
+Style rules are defined in `src/.editorconfig`.
+
+## Conventions
+
+- Developer behavior (tracing, agent debug logs, remote agent port) is controlled via
+  `src/CodyDevConfig.json`; this file is stripped from release builds.
+- During development you can supply your own Cody token via the `SourcegraphCodyToken`
+  environment variable, which overrides user settings and is never persisted.
+- CI (`.github/workflows/build.yml`) builds the agent, then runs `src/build.ps1`, then tests.