Initial planning docs: CLAUDE.md and ADRs 0000-0008

Captures up-front design decisions for RDBMS Playground:
stack (Rust + Ratatui + SQLite), input modes, project file
format, type vocabulary, undo snapshots and replay log,
sharing/export, and testing approach. ADR-0000 establishes
the ADR practice itself and mandates index upkeep alongside
any ADR change.

docs/adr/0001-language-and-tui-framework.md

@@ -0,0 +1,47 @@
+# ADR-0001: Language and TUI framework
+
+## Status
+
+Accepted
+
+## Context
+
+RDBMS Playground is a cross-platform terminal application aimed at
+learners. It needs to feel fast, polished, and colourful, install
+cleanly on Linux, macOS, and Windows, and ship as a single binary
+with no runtime dependencies.
+
+Beyond TUI rendering, the application has substantial SQL-handling
+needs: syntax highlighting, parsing user input to distinguish app
+DSL commands from SQL, rewriting simplified types into backend
+types, and analysing query plans for the teaching features.
+
+Two stacks were realistic candidates:
+
+1. **Rust + Ratatui + Crossterm** — strong cross-platform terminal
+   support, single static binary, mature ecosystem. Crucially,
+   `sqlparser-rs` is a high-quality dialect-aware SQL parser
+   directly applicable to the parsing, highlighting, and query
+   analysis features.
+2. **Go + Bubble Tea (Charm)** — excellent default aesthetics,
+   single static binary, easy distribution. Lacks an equivalent to
+   `sqlparser-rs`; SQL parsing would need to be written from
+   scratch or wrap a less suitable library.
+
+## Decision
+
+Use **Rust with Ratatui and Crossterm** for the TUI, with
+`sqlparser-rs` for SQL parsing and `rusqlite` for the database
+layer. Distribute as prebuilt binaries via GitHub releases plus
+package managers (`cargo binstall`, Homebrew, Scoop, `winget`).
+
+## Consequences
+
+- Single static binary on all three target platforms.
+- Strong fit between SQL-heavy features and the Rust SQL ecosystem
+  (`sqlparser-rs`, `rusqlite`).
+- Slightly steeper contributor on-ramp for developers unfamiliar
+  with Rust compared to Go.
+- TUI styling will require explicit work to match the polish that
+  Bubble Tea / Lipgloss give for free; budget for it in the design
+  pass.