docs: add project vision, MVP architecture spec, and reference material

- docs/VISION.md: product vision + feature catalogue (MVP / post-MVP / later)
- docs/specs/2026-06-02-mvp-architecture.md: MVP architecture + 16-entry decision log
- reference/: Spectrum 5.0 cataloguing + Riksantikvarieämbetet source material (build-time reference)
- CLAUDE.md: project guidance for Claude Code

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,25 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Status
+
+Freshly scaffolded Rust binary crate (edition 2024). `src/main.rs` is still the `cargo new` "Hello, world!" stub and `Cargo.toml` has no dependencies yet. There is no architecture to document — update this file as real structure emerges.
+
+## Commands
+
+```bash
+cargo build              # build
+cargo run                # run the binary
+cargo test               # run all tests
+cargo test <name>        # run a single test by name substring
+cargo +nightly fmt       # format — always nightly, not stable
+cargo clippy             # lint before committing
+```
+
+## Conventions
+
+- **CLI args & env vars:** use `clap` with the `derive` feature.
+- **Code navigation:** prefer the insikt LSP server over grep/glob — it resolves macro-generated symbols that text search misses. (insikt runs standalone, not via the gateway MCP.)
+- **Dependencies:** manage via the `cargo-mcp` server rather than editing `Cargo.toml` by hand.
+- **Formatting:** `cargo +nightly fmt` (nightly toolchain required).