docs: add docs-as-code process and one ADR per feature

docs/docs-as-code.md defines the workflow; docs/adr holds 31 ADRs
(retroactive, reconstructed from code and changelog) with a template and
index. docs/check-docs.sh validates ADR structure, index, cited code
paths, relative links and CLAUDE.md/AGENTS.md sync.

docs/adr/0023-github-release-update-check.md

@@ -0,0 +1,25 @@
+# 0023. Best-effort update check against GitHub releases
+
+- **Status:** Accepted
+- **Area:** Distribution
+- **Recorded:** 2026-11-03 (retroactive: reconstructed from code, comments and changelog)
+
+## Context
+
+Android builds are signed sideloads and desktop builds are single-file executables, so there is no store to notify users of fixes.
+
+## Decision
+
+`UpdateChecker.CheckAsync` compares the running version (single source: `<Version>` in the App csproj) with the latest GitHub release tag at startup. Any network or parse failure, or an up-to-date app, resolves to null; the UI prompts only when a newer release exists. The HTTP handler is injectable so tests never reach GitHub.
+
+## Consequences
+
+- Users learn about security fixes promptly; no telemetry is sent beyond the release API request.
+- The check leaks to GitHub that a wallet started; this is not covered by a Tor/proxy option.
+- The repository URL is hardcoded in the source and must be kept in sync if the project moves.
+
+## References
+
+- `src/Core/Net/UpdateChecker.cs`
+- `src/App/ViewModels/MainWindowViewModel.Update.cs`
+- `tests/PalladiumWallet.Tests/Net/UpdateCheckerTests.cs`