chore: rename project from idfoto to relicario

Sweeping rename across crates, CLI binary, WASM bindings, extension, docs,
and vault metadata paths. Git remote updated to relicario.git.

- crates/idfoto-{core,cli,wasm} -> crates/relicario-{core,cli,wasm}
- IdfotoError -> RelicarioError
- IDFOTO_IMAGE env var -> RELICARIO_IMAGE
- ~/.config/idfoto -> ~/.config/relicario
- .idfoto/ vault metadata dir -> .relicario/ (breaking; pre-release)
- Binary name idfoto -> relicario
- Extension wasm module idfoto_wasm -> relicario_wasm
- Storage key idfotoSettings -> relicarioSettings
- All doc filenames and content references updated

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/relicario-core/src/error.rs

@@ -0,0 +1,86 @@
+//! Unified error type for the relicario-core crate.
+//!
+//! Every fallible function in this crate returns [`Result<T>`], which is an alias
+//! for `std::result::Result<T, RelicarioError>`. Using a single error enum keeps the
+//! public API surface predictable and makes error handling in callers (CLI, WASM
+//! bindings, mobile FFI) straightforward.
+
+use thiserror::Error;
+
+/// All errors that can originate from relicario-core operations.
+///
+/// Variants are ordered roughly by the pipeline stage where they occur:
+/// KDF -> encryption -> decryption -> format parsing -> entry lookup -> image
+/// steganography -> serialization -> device keys.
+#[derive(Debug, Error)]
+pub enum RelicarioError {
+    /// The Argon2id key derivation failed. This typically means invalid KDF
+    /// parameters were supplied (e.g., memory cost below Argon2's minimum).
+    #[error("key derivation failed: {0}")]
+    Kdf(String),
+
+    /// XChaCha20-Poly1305 encryption failed. In practice this is extremely rare
+    /// -- the only realistic cause is an internal library error, since the cipher
+    /// accepts arbitrary-length plaintext.
+    #[error("encryption failed: {0}")]
+    Encrypt(String),
+
+    /// Authenticated decryption failed. This means either the wrong master key
+    /// was used (wrong passphrase or wrong reference image) or the ciphertext
+    /// was tampered with / corrupted in transit or at rest. The error message is
+    /// intentionally vague to avoid leaking information about which factor was
+    /// wrong (passphrase vs. image).
+    #[error("decryption failed: wrong key or corrupted data")]
+    Decrypt,
+
+    /// The binary ciphertext blob does not match the expected format (e.g.,
+    /// too short to contain the version byte + nonce + tag, or an unrecognized
+    /// version byte). This usually indicates file corruption or a version
+    /// mismatch between the writer and reader.
+    #[error("invalid vault format: {0}")]
+    Format(String),
+
+    /// A vault entry was looked up by ID but does not exist in the manifest.
+    /// The string payload is the missing entry ID.
+    #[error("entry not found: {0}")]
+    EntryNotFound(String),
+
+    /// A general error from the image steganography subsystem (imgsecret).
+    /// Covers issues like failing to decode the carrier JPEG or failing to
+    /// encode the output JPEG after modification.
+    #[error("imgsecret: {0}")]
+    ImgSecret(String),
+
+    /// The carrier image is too small to hold the embedded secret with
+    /// sufficient redundancy. The embed region (central 70% of the image)
+    /// must contain at least `BLOCKS_PER_COPY * MIN_COPIES` 8x8 blocks.
+    #[error("image too small: need at least {min_width}x{min_height}, got {actual_width}x{actual_height}")]
+    ImageTooSmall {
+        min_width: u32,
+        min_height: u32,
+        actual_width: u32,
+        actual_height: u32,
+    },
+
+    /// Secret extraction from a JPEG failed. This can mean:
+    /// - The image never had a secret embedded in it.
+    /// - The image was recompressed below Q85, destroying the QIM watermarks.
+    /// - The image was cropped beyond the 15% crumple zone.
+    /// - Majority-vote confidence fell below the 60% threshold on one or more bits.
+    #[error("extraction failed: no valid secret found in image")]
+    ExtractionFailed,
+
+    /// JSON serialization or deserialization of an entry or manifest failed.
+    /// Wraps [`serde_json::Error`] transparently via `#[from]`.
+    #[error("json error: {0}")]
+    Json(#[from] serde_json::Error),
+
+    /// An error related to device ed25519 key operations. Device keys are
+    /// separate from the vault KDF -- revoking a device does not require
+    /// rotating the passphrase or reference image.
+    #[error("device key error: {0}")]
+    DeviceKey(String),
+}
+
+/// Crate-wide result alias, reducing boilerplate in function signatures.
+pub type Result<T> = std::result::Result<T, RelicarioError>;