docs: add scope headers + Next: footers to all tour docs

Each of the eight tour docs (README, DESIGN, docs/CRYPTO,
docs/FORMATS, docs/SECURITY, crates/relicario-core/ARCHITECTURE,
crates/relicario-cli/ARCHITECTURE, extension/ARCHITECTURE) now
declares its scope in a blockquote under its H1 and ends with a
single-line "Next:" pointer to the next doc in the canonical
reading order: README → DESIGN → CRYPTO → FORMATS → SECURITY →
core → cli → extension.

Also trimmed README's mid-section "Architecture" stub to a one-
paragraph pointer at DESIGN.md (was duplicating cross-codebase
content and referencing a non-existent docs/architecture/ tree).

Renamed docs/CRYPTO.md's H1 from "Relicario — Architecture" to
"Relicario — Crypto Pipeline" to match the file's renamed scope.

Spec: docs/superpowers/specs/2026-05-30-doc-structure-redesign-design.md

docs/CRYPTO.md

@@ -1,4 +1,6 @@
-# Relicario — Architecture
+# Relicario — Crypto Pipeline
+
+> **Audience:** anyone evaluating or auditing the crypto. This doc owns Argon2id parameters and rationale, XChaCha20-Poly1305 rationale, vault creation/unlock flow diagrams, DCT-steganography embed and extract flows, and the high-level encrypted-file-format diagram. **Does NOT own:** byte-level schemas or JSON shapes (see [FORMATS.md](FORMATS.md)), attacker scenarios (see [SECURITY.md](SECURITY.md)), or per-module crypto implementation (see [../crates/relicario-core/ARCHITECTURE.md](../crates/relicario-core/ARCHITECTURE.md)).
 
 ## System Overview
 
@@ -274,3 +276,7 @@ Stolen device:               ████░░░░░░░░░░░░░
 
 Both factors compromised:    game over (same as every password manager)
 ```
+
+---
+
+**Next:** [FORMATS.md](FORMATS.md) — the byte-level wire formats.

docs/FORMATS.md

@@ -1,5 +1,7 @@
 # Relicario Wire Formats
 
+> **Audience:** anyone implementing a compatible client or reading raw vault bytes. This doc owns the `.enc` blob layout, `params.json` / `salt` / `devices.json` / `revoked.json` shapes, the manifest JSON schema, the `.relbak` envelope, item-ID formats, and the settings JSON schema. **Does NOT own:** why these formats look this way (see [CRYPTO.md](CRYPTO.md)), threat model around them (see [SECURITY.md](SECURITY.md)), or Rust struct internals (see [../crates/relicario-core/ARCHITECTURE.md](../crates/relicario-core/ARCHITECTURE.md)).
+
 > Quick-reference for the load-bearing binary and JSON formats. Check this file before touching serialization, versioning, or storage layout code. Full diagrams and invariants live in the per-crate `ARCHITECTURE.md` files.
 
 ## Encrypted blob (`.enc` files)
@@ -100,3 +102,7 @@ u64_be(len(passphrase)) || passphrase_bytes || u64_be(32) || image_secret
 ```
 
 NFC-normalized before hashing. Covered in `crypto.rs:229-236` and tested in `tests/format_v2.rs:44-54`.
+
+---
+
+**Next:** [SECURITY.md](SECURITY.md) — the threat model.

docs/SECURITY.md

@@ -1,5 +1,7 @@
 # Relicario Security Model
 
+> **Audience:** auditors and curious users. This doc owns the threat model, attacker-scenarios table, device-authentication model, env-var trust surface, and known limitations. **Does NOT own:** crypto primitive details (see [CRYPTO.md](CRYPTO.md)), wire formats (see [FORMATS.md](FORMATS.md)), or implementation (see [../crates/relicario-core/ARCHITECTURE.md](../crates/relicario-core/ARCHITECTURE.md) and [../crates/relicario-cli/ARCHITECTURE.md](../crates/relicario-cli/ARCHITECTURE.md)).
+
 ## Cryptographic Protection
 
 Relicario uses two-factor vault decryption:
@@ -102,3 +104,7 @@ standard `--release` profile).
 | `RELICARIO_TEST_PASSPHRASE` | Bypass the `rpassword` prompt during integration tests. |
 | `RELICARIO_TEST_ITEM_SECRET` | Bypass the `rpassword` prompt for item-secret fields during integration tests. |
 | `RELICARIO_TEST_BACKUP_PASSPHRASE` | Bypass the `rpassword` prompt for backup export/restore passphrases during integration tests. |
+
+---
+
+**Next:** [../crates/relicario-core/ARCHITECTURE.md](../crates/relicario-core/ARCHITECTURE.md) — implementation, starting with the platform-agnostic core.