fix(import): tolerate common file variations and say where a file breaks (#19) - #67

Refs #19. Doesn't close it: we still have no sample files from the reporter, so this covers what was reproducible without them.

Why

Probing the BeerXML parser showed one odd value failed the whole import with an unlocated serde message: a decimal comma (5,5), a lowercase enum (boil), a common synonym (Whirlpool, Malt), or a hop without <ALPHA>. BeerJSON imports reported Ajv's first error, often a combinator or a property-less "must NOT have additional properties".

BeerXML (werb-beerxml: app import via WASM, and the CLI)

• Numbers read a decimal comma; with a point present, commas are thousands separators. Failures say not a number: "<raw>".
• Enums go through LenientEnum: case, spacing and punctuation ignored, plus synonyms (Whirlpool / Hop stand / Flameout → Aroma, Malt → Grain, Whole / Cones → Leaf). Unknown values read as absent and the converter applies its default.
• Missing hop ALPHA / AMOUNT, fermentable or misc AMOUNT read as 0, like an empty element already did.
• serde_path_to_error locates failures: Error::Invalid { location } with a 1-based XPath, e.g. /RECIPES/RECIPE[1]/HOPS/HOP[2]/AMOUNT: not a number: "lots". JolieBulle JSON errors carry their field path.

BeerJSON (@werb/validate: file import and GitHub Pull)

• stripNulls: null optional properties mean absent.
• describeErrors: the deepest, most telling error, naming the missing or unknown property, or the value and the allowed ones.

Tests

• Rust: lenient numbers / enums / missing alpha, located errors, JolieBulle path.
• @werb/validate: stripNulls, describeErrors (enum, required, type).
• Desktop: WASM import of a loose file and a broken one; BeerJSON with nulls and with a missing property.
• e2e through the file picker: loose BeerXML imports, broken BeerXML shows the XPath, broken BeerJSON names the property. Full suite 35/35 locally, Rust workspace green, lint clean.