feat(server): display custom list metadata (e.g. nutrition) on recipe pages

[Tloxipeuhca]

Closes #459

Summary

• Any non-standard YAML frontmatter key whose value is a list (e.g. nutrition:) is now shown as its own line below the tags on the recipe and menu pages — one line per family, no code changes needed to support new families.
• nutrition: entries get a matching icon (Tabler Icons, MIT license, inlined as SVG — no new dependency) picked by keyword in the unit text: kcal/energy → flame, protein → meat, lipid/fat → droplet, sugar → candy, fiber → wheat. Unrecognized families/units render as a plain bullet.
• The recipe list page shows a compact 🔥 X kcal badge next to the tags when a recipe has nutrition: with a kcal entry.
• Entries are written as value%unit (e.g. 258%kcal) and displayed as 258 kcal.
• New: nutrition: also supports a mapping form (nutrition: {kcal: 234, proteins: 9.8, ...}) alongside the original list form, with per-field unit inference (kcal → kcal, everything else → g) and 3 additional nutrient fields (saturated-fat, carbohydrates, salt) with matching icons.
• New: a file family (created-by/created-at/modified-by/modified-at) is now recognized, with person/calendar/pencil/history icons.
• New: nutrient and file-metadata field names are translated into the viewer's UI language via the existing Fluent i18n system, across all 7 supported locales (de-DE, en-US, es-ES, eu-ES, fr-FR, nl-NL, sv-SE).
• New: a YAML key prefixed with . is hidden from the recipe page, at either the family level (.file:) or a single mapping entry (.lipids:) — useful for metadata you want in the file but not shown to readers.
• Refactored per-family rendering into src/web/family_renderers/ (mod.rs + generic.rs + nutrition.rs + file.rs): a small FamilyRenderer trait with a generic fallback, and an explicit renderer_for() registry so adding a future specific renderer only touches one match arm.
• Documented the convention in docs/server.md ("Custom Metadata Families").

Test plan

• cargo build, cargo clippy --all-targets (clean, no warnings), cargo fmt --check — all pass.
• Manually tested with a real ~250-recipe collection using both the list and mapping nutrition: forms, via cargo run -- server:
  • Recipe detail page renders one "Nutrition" line with correct icons for kcal/protein/lipid/carbs/salt/sugar/fiber, in both YAML forms.
  • file:/meta: metadata renders with the expected icons and translated labels.
  • Switching the UI locale correctly translates nutrient/file-metadata labels.
  • Keys prefixed with . (family-level and entry-level) are correctly hidden.
  • Nested non-list, non-mapping metadata is correctly ignored — does not render as a spurious line.
  • List page shows the kcal badge next to tags.
• Screenshots on request if useful for review.

🤖 Generated with Claude Code

[Tloxipeuhca]

Update: mapping form, i18n, dot-hiding, generic fallback

Following review discussion, this PR now also supports:

Mapping form + 3 new nutrition fields

nutrition: can now be written as a mapping (recommended) instead of a list, with per-field unit inference (kcal → kcal, everything else → g):

nutrition:
  kcal: 234
  proteins: 9.8
  lipids: 17.6
  saturated-fat: 6.2
  carbohydrates: 18.4
  sugars: 8.9
  fibers: 0.9
  salt: 1.85

The original list form (- "258%kcal") still works too, unchanged.

New file: family

file:
  created-by: Yannick
  created-at: 2026-08-20
  modified-by: Yannick
  modified-at: 2026-08-24

Renders as its own line with person/calendar/pencil/history icons and a translated "Label: value" per entry. file: and meta: are both accepted as the family key.

Generic fallback (any other family, still works exactly as before)

allergens:
  - gluten
  - tree nuts
origin:
  country: France
  region: Alsace

Any YAML key that isn't nutrition or file/meta still renders automatically — list entries as-authored, mapping entries as field: value, no icon, no code change required. nutrition and file/meta are just the two families that opted into specific icons/formatting.

.-prefix hiding

Prefix a key with . to hide it from the recipe page:

.internal-notes:
  - draft, not ready for print
nutrition:
  kcal: 234
  .lipids: 17.6   # hidden; the rest of the nutrition line still shows

Works at the family level (.internal-notes: hides the whole line) and at the single-entry level inside a mapping (.lipids: hides just that one chip).

i18n

Nutrient names and the file/meta labels are translated into the viewer's UI language across all 7 supported locales, including correct French typography (space before :).

Refactor

Renderer logic moved to src/web/family_renderers/ (mod.rs + generic.rs + nutrition.rs + file.rs) — a small FamilyRenderer trait, generic default, and an explicit renderer_for() registry so a future specific renderer is one match arm + one file.

cargo build, cargo clippy --all-targets, cargo fmt --check all clean.

[Tloxipeuhca]

Screenshot of the mapping-form nutrition + file metadata rendering (fr-FR locale):

1. Recipe list page — the Tarte Flambée card shows a compact 🔥 1443 kcal badge next to its tags, pulled from the nutrition.kcal mapping entry; other cards without nutrition: show no badge.
2. English locale (Accept-Language: en-US) — same recipe, same FILE/NUTRITION lines in English (Modified at, Modified by, fat, saturated fat, carbohydrates, sugars, fiber, proteins, salt).
3. French locale (Accept-Language: fr-FR) — recipe page showing the FILE line (Modifié le : 2026-08-24, Modifié par : Yannick, note the French space before :) and the NUTRITION line with all 8 fields translated (lipides, graisses saturées, glucides, sucres, fibres, protéines, sel) plus their icons.

[Tloxipeuhca]

Closes #459

[dubadub]

Thanks for that, will review in a day or two