V1.12.1: each library entry goes into a campaign once

- A weapon, item, spell or monster from the library can be added to a
  campaign once. Adding it again is refused: "Longsword is already in
  this campaign."
- The library list leaves out what the campaign already has, so what is
  left is what can still be added. When nothing is left it says so.
- An entry counts as added while the campaign has one by that name,
  whatever its capitals. Rename or delete the campaign's copy and the
  library offers it again. This also covers what a world's seed put in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ITEMS.md

@@ -53,7 +53,9 @@ The pool is the "Items Pool" card on the campaign page (DM only).
   worn gear such as a Ring of Protection, and common supplies. Each is copied
   into the pool with its effects already set (Chain Mail: +6 AC, −10 Speed,
   and a note about Stealth), at starting level 1 and not ticked as a starting
-  option. The copy is yours to change. The full list is in section 10.
+  option. The copy is yours to change. The full list is in section 10. Each
+  can be added once: an item the pool already has by that name is left out of
+  the library list, and comes back if the pool's item is renamed or deleted.
 - **Effects:** the "Effects" button on an item's row. The row shows what the
   item does under its name.
 - **Changing:** starting level, growth (when the item has dice) and the

docs/MONSTERS.md

@@ -57,6 +57,9 @@ The list is the "Monsters" card on the campaign page (DM only).
   scores, special trait and notes. Only name, AC and HP must be typed; speed
   starts at 30, attack bonus at 0 and each ability score at 10.
 - **Adding from the bestiary:** "📚 From Library" copies a complete stat block.
+  Each monster can be added once: one the campaign already has by that name is
+  left out of the list, and comes back if the campaign's monster is renamed or
+  deleted.
 - **Changing:** "Edit" on a monster's row opens the same form filled in.
   Saving changes the template, and copies already in encounters show the new
   stat block straight away; their current HP is left alone.

docs/SPELLS.md

@@ -107,6 +107,10 @@ one shown.
 A spell added from the library is **not** a starting option until ticked. The
 library has nothing above level 5; add higher spells by hand.
 
+Each library spell can be added once. A spell the list already has by that
+name is left out of the library list, and comes back if the campaign's spell
+is renamed or deleted.
+
 ## 4. Granting spells to characters
 
 On a character's sheet, the DM picks a spell from the list and clicks Grant.

docs/WEAPONS.md

@@ -86,6 +86,10 @@ growth, and **not** ticked as a starting option. Change those in the table
 afterwards. Every library weapon is listed in
 [section 12](#12-the-complete-weapon-library).
 
+Each library weapon can be added once. A weapon the pool already has by that
+name is left out of the library list, and comes back if the pool's weapon is
+renamed or deleted.
+
 ## 4. Giving weapons to characters
 
 On a character's sheet, the DM picks a weapon from the pool and clicks Give.