feat: personal and private packing categories

[robbedekien]

Description

Adds shared/personal/private packing categories so trip members can keep
items personal to themselves (own check state, visible to others) or
fully private (owner-only). Templates round-trip shared and personal
categories; private items stay with their owner.

Server:

• Migration 123 promotes packing_items.category text → typed
  packing_categories table with type ∈ {shared, personal, private},
  adds packing_item_checks for per-user check state on non-shared
  categories, and re-keys packing_category_assignees from category
  name to category_id.
• Migration 124 adds type to packing_template_categories so
  applyTemplate can recreate personal categories as personal owned by
  the applying user.
• Routes: 4 new endpoints under /packing/categories. Per-user check
  toggles broadcast actor-only (Option B) so personal/private state
  doesn't leak to other clients.
• Trip clone copies shared categories only; share links filter to shared.
• MCP gains list/create/update/delete_packing_category tools.

Client:

• Type pill in each category header, "Make shared/personal/private"
  menu items, type picker on Add Category, hint line under Save as
  Template explaining private exclusion.
• Tooltips with sharper copy ("Visible to everyone, but each person
  tracks their own checks." etc) localised in 15 languages.
• Robust state sync: panel re-fetches /categories when items
  reference unknown ids (covers post-applyTemplate flow); category
  delete mirrors the server-side cascade in the store.

Documentation:

• Updated wiki/Packing-Lists.md with the new category types and
  template behavior.
• Updated wiki/MCP-Addon-Tools.md with the 4 new tools.

Tests:

• Server: 12 new packing tests (PACK-016..021, 017d, 017e) covering
  category CRUD, type validation, duplicate-409, private-category
  isolation, per-user check state, shared→personal conversion, and
  the save→apply round-trip preserving personal type for the applying
  user. All 36 integration + 30 unit packing tests pass.
• Client: factory now derives a deterministic category_id per
  category name; existing 67 PackingListPanel tests pass plus updated
  assertions for the new POST/PATCH/DELETE category endpoints.

Related Issue or Discussion

https://discord.com/channels/1488298068427411591/1491808813240684615

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Checklist

• I have read the Contributing Guidelines
• My branch is up to date with dev
• This PR targets the dev branch, not main (wiki-only PRs are exempt)
• I have tested my changes locally
• I have added/updated tests that prove my fix is effective or that my feature works
• I have updated documentation if needed

Demo

Below are 2 screenshots of different users viewing the same trip. Showcasing separate checked state and private categories