Feature: share a character with its homebrew embedded in the link

[codeGlaze]

Problem

A shared character link only carries the character id. The homebrew content the character references (custom races, classes, subclasses, spells, feats, backgrounds) lives in the sharer's local .orcbrew, so a recipient who doesn't own it sees the sheet render as missing content.

Feature

Add a share link that embeds the exact homebrew the character uses:

• The character's dependency closure (direct + subclass->class, subrace->race, granted spells, race->language, reverse spell-list membership) is extracted and gzip-compressed into the URL fragment.
• On open, it decodes through untrusted-input gates (input cap, decompression-bomb guard, safe reader with no eval, fail-closed structural whitelist) and the same per-item spec load-floor a file import uses, into an ephemeral view-once overlay that renders for that view only and is never written to the recipient's library.
• A banner offers Keep in my library and flags any content that collides by name with the recipient's own (shared version wins on the shared sheet; their copy is untouched).
• Content is never stripped to fit: the full payload rides along, or (only when too large for any link) a file fallback is offered.

Custom magic items are handled separately (see the companion issue).