docs: fix crypto/format drift — version byte 0x02, AttachmentId 32 hex, DCT 5-50

Punch items from doc audit:
- docs/ARCHITECTURE.md: encrypted file format diagram said version byte
  0x01; actual VERSION_BYTE is 0x02 (crypto.rs:59) and 0x01 is rejected
  with UnsupportedFormatVersion.
- docs/ARCHITECTURE.md: DCT embedding diagram said "Repeat secret 20+
  times" and "positions 4-15"; actual is MIN_COPIES (5) to 50 copies
  chosen by capacity, embedded in zig-zag positions 6-17
  (imgsecret.rs:78, 99-104, 530-537).
- FORMATS.md: AttachmentId table said 16 hex chars / 8 bytes; actual is
  32 hex chars / first 16 bytes of SHA-256 (ids.rs:59-69).
- FORMATS.md: ManifestEntry schema missing r#type field; updated to list
  all ten fields in declared order with serde decorations noted
  (manifest.rs:21-38).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

FORMATS.md

@@ -45,7 +45,7 @@ Parsed via `ParamsFile { kdf: KdfParams }` in `session.rs`. The `kdf` nesting is
 Decrypts to JSON matching the `Manifest` struct (`manifest.rs`).
 
 - **Schema version:** `MANIFEST_SCHEMA_VERSION = 2` (`manifest.rs:12`). v1 manifests (pre-typed-items) fail to parse and are not supported.
-- **`ManifestEntry` fields:** `id`, `title`, `tags`, `favorite`, `group`, `icon_hint`, `modified`, `trashed_at`, `attachment_summaries`.
+- **`ManifestEntry` fields** (declared order in `manifest.rs:21-38`): `id`, `type`, `title`, `tags`, `favorite`, `group`, `icon_hint`, `modified`, `trashed_at`, `attachment_summaries`. The `type` field is `r#type: ItemType` in Rust but serializes as the bare JSON key `"type"` (no serde rename — `r#` is just the raw-identifier escape). `group`, `icon_hint`, and `trashed_at` are `#[serde(skip_serializing_if = "Option::is_none")]`; `tags`, `favorite`, and `attachment_summaries` use `#[serde(default)]`.
 - The manifest is rebuilt from scratch on every `upsert` — it can never drift from the source-of-truth item files.
 - Supports case-insensitive title/tag search without decrypting any item.
 
@@ -75,9 +75,9 @@ Commits by `public_key` at or after `revoked_at` (Unix seconds) are rejected by
 |---|---|---|---|
 | `ItemId` | 16 hex chars | 64 bits | `OsRng` |
 | `FieldId` | 16 hex chars | 64 bits | `OsRng` |
-| `AttachmentId` | 16 hex chars | content-addressed | first 8 bytes of `SHA-256(plaintext)` |
+| `AttachmentId` | 32 hex chars | 128 bits | first 16 bytes (32 hex chars) of `SHA-256` over the plaintext |
 
-`AttachmentId` is content-addressed — identical plaintexts deduplicate in git automatically.
+`AttachmentId` is content-addressed — identical plaintexts deduplicate in git automatically. The 128-bit truncation (`ids.rs:59-69`) was widened from 64 bits per audit I2/B4 to put birthday-collision risk out of reach.
 
 ## `.relbak` backup format
 

docs/ARCHITECTURE.md

@@ -161,11 +161,14 @@ master_key ────────►│  XChaCha20       │──────
                     │  selected block: │
                     │                  │
                     │  QIM embed bits  │
-                    │  in positions    │
-                    │  4-15 (mid-freq) │
+                    │  in zig-zag      │
+                    │  positions 6-17  │
+                    │  (mid-frequency) │
                     │                  │
                     │  Repeat secret   │
-                    │  20+ times       │
+                    │  MIN_COPIES (5)  │
+                    │  to 50 times,    │
+                    │  by capacity     │
                     └────────┬─────────┘
                              │
                              ▼
@@ -181,6 +184,8 @@ master_key ────────►│  XChaCha20       │──────
                      carries 256-bit secret)
 ```
 
+The redundancy count is chosen at embed time based on available DCT capacity: `num_copies = (total_blocks / BLOCKS_PER_COPY).min(50)`, with `BLOCKS_PER_COPY = 22` and a floor of `MIN_COPIES = 5` (`crates/relicario-core/src/imgsecret.rs:78,530-537`). Images that cannot fit at least 5 copies are rejected before embed. Majority voting across these copies at extract time requires ≥ 60 % confidence per bit.
+
 ## Extraction (with crop recovery)
 
 ```
@@ -214,10 +219,12 @@ Input JPEG (possibly re-encoded or cropped)
 ┌─────────┬────────────────────────┬──────────────────┬──────────────────┐
 │ version │         nonce          │    ciphertext     │    auth tag      │
 │ 1 byte  │       24 bytes         │    N bytes        │    16 bytes      │
-│  0x01   │ random per write       │ XChaCha20 stream  │ Poly1305 MAC     │
+│  0x02   │ random per write       │ XChaCha20 stream  │ Poly1305 MAC     │
 └─────────┴────────────────────────┴──────────────────┴──────────────────┘
 ```
 
+`VERSION_BYTE = 0x02` (`crates/relicario-core/src/crypto.rs:59`). Blobs starting with any other byte are rejected with `UnsupportedFormatVersion { found, expected: 0x02 }`. The legacy `0x01` format from the pre-typed-items era is no longer supported.
+
 ## Crate Architecture
 
 ```