feat(dist): crates.io + binstall + Windows install.ps1 + license files

Distribution prep on the road to public availability (plan steps 2–3a).

- Cargo.toml: publish-ready (drop publish=false; homepage/keywords/
  categories/exclude) + [package.metadata.binstall] with per-target
  overrides (linux-gnu->musl, windows-msvc->gnu/gnullvm). dry-run clean.
- scripts/install.ps1: Windows `irm | iex` one-liner — written but
  untested here (no PowerShell; validate on Windows). README Windows block.
- README.md (new); LICENSE-MIT + LICENSE-APACHE (dual, (c) Lazy
  Evaluation Ltd); CONTRIBUTING.md (inbound=outbound dual-license note).
- ADR-0055 Amendment 1 (install.ps1), ADR-0056 (crates.io/binstall),
  README index + plan updates.

The actual `cargo publish` remains a gated maintainer step (token,
irreversible) at a new tagged release; real cargo-binstall validation
pending.

Cargo.toml

@@ -5,8 +5,17 @@ edition = "2024"
 description = "A cross-platform TUI playground for learning relational databases."
 license = "MIT OR Apache-2.0"
 repository = "https://git.lazyeval.net/oli/rdbms-playground"
+homepage = "https://relplay.org"
 readme = "README.md"
-publish = false
+keywords = ["database", "sql", "tui", "learning", "playground"]
+categories = ["command-line-utilities", "database"]
+# Keep the published crate to the code that builds the binary — the website,
+# decision records, and CI plumbing are repo-only (ADR-0056).
+exclude = ["/website", "/docs", "/.gitea", "/.codegraph"]
+# `publish = false` removed (ADR-0056): the crate is intended for
+# crates.io. The actual `cargo publish` is a deliberate, irreversible
+# maintainer step (needs the crates.io token) — do it at a tagged release
+# whose assets the binstall metadata below points at.
 
 [dependencies]
 anyhow = "1.0.102"
@@ -85,3 +94,33 @@ nursery = { level = "warn", priority = -1 }
 module_name_repetitions = "allow"
 missing_errors_doc = "allow"
 missing_panics_doc = "allow"
+
+# cargo-binstall (ADR-0056): let `cargo binstall rdbms-playground` fetch the
+# prebuilt release binary instead of compiling from source. Our release assets
+# are BARE binaries (no archive) named `rdbms-playground-v<version>-<target>`
+# (`.exe` on Windows) with `.sha256` sidecars (ADR-ci-003), so `pkg-fmt = "bin"`.
+# `{ version }` excludes the leading `v`, so the template spells `v{ version }`.
+#
+# Target mapping: macOS host triples match our asset triples directly. But we
+# ship the fully-static *-linux-MUSL build (glibc hosts are *-linux-gnu) and
+# *-windows-GNU/GNULLVM (most Windows hosts are *-msvc), so those common host
+# triples need explicit overrides pointing at the asset we actually publish.
+#
+# NOTE: unverified against a real `cargo binstall` run (binstall isn't a dep and
+# nothing is on crates.io yet) — validate at the first publish + matching release.
+[package.metadata.binstall]
+pkg-url = "{ repo }/releases/download/v{ version }/{ name }-v{ version }-{ target }{ archive-suffix }"
+pkg-fmt = "bin"
+bin-dir = "{ bin }{ binary-ext }"
+
+[package.metadata.binstall.overrides.x86_64-unknown-linux-gnu]
+pkg-url = "{ repo }/releases/download/v{ version }/{ name }-v{ version }-x86_64-unknown-linux-musl"
+
+[package.metadata.binstall.overrides.aarch64-unknown-linux-gnu]
+pkg-url = "{ repo }/releases/download/v{ version }/{ name }-v{ version }-aarch64-unknown-linux-musl"
+
+[package.metadata.binstall.overrides.x86_64-pc-windows-msvc]
+pkg-url = "{ repo }/releases/download/v{ version }/{ name }-v{ version }-x86_64-pc-windows-gnu.exe"
+
+[package.metadata.binstall.overrides.aarch64-pc-windows-msvc]
+pkg-url = "{ repo }/releases/download/v{ version }/{ name }-v{ version }-aarch64-pc-windows-gnullvm.exe"