fix(dialog): name the sharee "recipient" everywhere

[skjnldsv]

The dialog called the same thing people, participants and recipients. Settled on recipient, which the API and the code already use:

• "Add people" → "Add recipient"
• "Remove participant" → "Remove recipient"
• "Switching to a public link removes %n invited person/people from this share." → "…removes %n recipient/recipients…"

"Note to recipients" comes from the backend property, so it is already right.

Fixes #279

One I did not touch: the "Invited people" tab. It labels a share type rather than the sharee, and it pairs with "Anyone", so renaming it looked like a design call rather than a wording cleanup — @susnux @kra-mo, say the word and I will fold it in.

The files_sharing sidebar in server has its own "Remove participant" that should follow; I can do that once this lands.

👾 This pull request was assisted by Claude Code, commits carry an Assisted-by trailer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.91%. Comparing base (6e6c125) to head (60dc772).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #288   +/-   ##
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  Coverage   79.91%   79.91%           
=======================================
  Files          27       27           
  Lines         727      727           
  Branches      202      202           
=======================================
  Hits          581      581           
  Misses        127      127           
  Partials       19       19           

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