v0.5.4: code-cleanup pass (AppError, figment config, encoding dedup, typed status, deps)

Final cleanup before hardware testing. No behaviour changes; 248 tests green,
clippy clean.

#1  AppError newtype (http-api/src/error.rs) with one IntoResponse mapping
    (NotFound→404, Invalid→400, _→500) + From<core::Error>/From<io::Error>.
    Converted the clearly-safe handlers (sso_put, unattended_upload,
    branding_clear) to `?`; intentionally left handlers with bespoke
    status semantics (Invalid→404 on category, 409 on duplicate share /
    open upload) explicit so no asserted status changes.
#2  figment-based Config::load (defaults → TOML → env). Keeps the historical
    flat OPENPXE_* names (Unraid/entrypoint compatible) AND adds the nested
    OPENPXE_SECTION__FIELD form; now covers every field (apply_env had
    silently skipped unattended_dir + bind addrs). 6 Jail tests prove
    backward-compat. Removed the hand-rolled apply_env.
#3  thiserror 1→2; dropped unused mime/mime_guess/once_cell deps.
#4  Re-evaluated: Duration::from_hours/from_mins are stable on the pinned
    1.95 toolchain and clippy prefers them — kept the readable form
    (the "unstable" premise didn't hold; MSRV is intentionally 1.95).
#5  insta snapshot of the rendered iPXE menu (version-filtered) + wiremock
    coverage of the SAML metadata-URL fetch (200 + non-2xx).
#6  api_status → typed StatusResponse struct (was a 25-key json! blob) with
    a full_flow guard test asserting every UI key + the started_at string
    shape. Deferred the /api/docs typed conversion (lowest value, highest
    churn, zero functional benefit).
#7  pct_encode/xml_escape de-duplicated into openpxe_core::encoding (were
    copied across app.rs + the SAML modules). No new crates.
#8  UploadSessions registry → parking_lot::RwLock (sync, never held across
    .await); per-session lock stays tokio::Mutex.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

Cargo.toml

@@ -12,7 +12,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.5.3"
+version = "0.5.4"
 edition = "2021"
 rust-version = "1.95"
 license = "MIT OR Apache-2.0"
@@ -36,25 +36,25 @@ tower = "0.5"
 tower-http = { version = "0.6", features = ["fs", "trace", "cors", "limit"] }
 hyper = "1.4"
 reqwest = { version = "0.12", default-features = false, features = ["rustls-tls", "stream", "json"] }
-mime = "0.3"
-mime_guess = "2.0"
 
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 toml = "0.8"
+# v0.5.4: layered config (TOML file + env). Pure-Rust, no C deps; keeps the
+# static-musl build OpenSSL-free. Replaces the hand-rolled apply_env mapping.
+figment = { version = "0.10", features = ["toml", "env"] }
 
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
 
 anyhow = "1.0"
-thiserror = "1.0"
+thiserror = "2.0"
 clap = { version = "4.5", features = ["derive", "env"] }
 uuid = { version = "1.10", features = ["v4", "serde"] }
 time = { version = "0.3", features = ["serde", "serde-human-readable", "formatting", "macros"] }
 sha2 = "0.10"
 hex = "0.4"
 bcrypt = "0.15"
-once_cell = "1.19"
 parking_lot = "0.12"
 rust-embed = { version = "8.5", features = ["include-exclude"] }