refactor(core,cli): migrate CLI parsers to relicario-core, parse.rs becomes shim

Plan B Phase 7 sub-step 2 — moves the bodies of parse_month_year,
base32_decode_lenient, guess_mime from crates/relicario-cli/src/parse.rs
to relicario-core. The CLI's parse.rs becomes a 19-line shim re-exporting
the new core API.

New core surface:
- time::MonthYear::parse (Result<_, RelicarioError>)
- mime::guess_for_extension (new mime module)
- item_types::TotpConfig::parse_secret — Zeroizing<Vec<u8>> wrapper
  over base32::decode_rfc4648_lenient

base32 module promoted from pub(crate) to pub so non-core consumers
(CLI shim, future Phase 8 WASM exports) can reach it. New
RelicarioError::InvalidMonthYear(String) for the parse error path
(mirrors sub-step 1's InvalidBase32). MonthYear::new keeps its
&'static str error type — bringing it to RelicarioError is DEV-A's P3.

CLI callsites unchanged (commands/{add,edit,attach}.rs); RelicarioError
auto-converts to anyhow::Error at ? boundaries.

cargo test --workspace: green (core 143, +7 from new tests)
cargo clippy --workspace: silent

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

crates/relicario-cli/src/parse.rs

@@ -1,47 +1,19 @@
-//! Small parsers used by the CLI (`MM/YY[YY]`, lenient base32, MIME guess).
-//!
-//! Phase 7 of the CLI restructure migrates these to `relicario-core` and
-//! turns this file into a thin re-export shim. They live here for now so
-//! the Phase 1 relocation stays mechanical.
+//! Thin shims over `relicario-core`'s migrated parsers, kept here so existing
+//! CLI callsites need no import churn. Plan B Phase 7 moved the bodies into
+//! `relicario_core::{time::MonthYear::parse, base32::decode_rfc4648_lenient,
+//! mime::guess_for_extension}`.
 
-use anyhow::{Context, Result};
+use anyhow::Result;
+use relicario_core::MonthYear;
 
-pub(crate) fn parse_month_year(s: &str) -> Result<relicario_core::MonthYear> {
-    // Accepts MM/YYYY or MM-YYYY or MM/YY.
-    let (m_str, y_str) = s.split_once(['/', '-'])
-        .ok_or_else(|| anyhow::anyhow!("expected MM/YYYY"))?;
-    let month: u8 = m_str.parse().context("invalid month")?;
-    let year: u16 = if y_str.len() == 2 {
-        2000 + y_str.parse::<u16>().context("invalid 2-digit year")?
-    } else {
-        y_str.parse().context("invalid year")?
-    };
-    Ok(relicario_core::MonthYear { month, year })
+pub(crate) fn parse_month_year(s: &str) -> Result<MonthYear> {
+    Ok(MonthYear::parse(s)?)
 }
 
 pub(crate) fn guess_mime(filename: &str) -> String {
-    let lower = filename.to_ascii_lowercase();
-    match lower.rsplit_once('.').map(|(_, ext)| ext).unwrap_or("") {
-        "pdf"        => "application/pdf",
-        "png"        => "image/png",
-        "jpg" | "jpeg" => "image/jpeg",
-        "txt"        => "text/plain",
-        "json"       => "application/json",
-        _            => "application/octet-stream",
-    }.to_string()
+    relicario_core::mime::guess_for_extension(filename).to_string()
 }
 
 pub(crate) fn base32_decode_lenient(s: &str) -> Result<Vec<u8>> {
-    let cleaned: String = s.chars()
-        .filter(|c| !c.is_whitespace())
-        .collect::<String>()
-        .to_ascii_uppercase()
-        .trim_end_matches('=')
-        .to_string();
-    let padded = {
-        let rem = cleaned.len() % 8;
-        if rem == 0 { cleaned } else { format!("{}{}", cleaned, "=".repeat(8 - rem)) }
-    };
-    data_encoding::BASE32.decode(padded.as_bytes())
-        .map_err(|e| anyhow::anyhow!("invalid base32: {e}"))
+    Ok(relicario_core::base32::decode_rfc4648_lenient(s)?)
 }