Make custom Tags relation filterable on all four entities

Expose the custom many-to-many CTag "Tags" relation as a linkMultiple
field (cTags) so it can be added to the list-view Search Filters, and
build the full Tags setup on Lead from scratch in parity with the others.

Opportunity / Contact / Account (relation already existed):
- add fields.cTags (linkMultiple) to entityDefs
- add cTags to the Search-Filters layout (Opportunity appended, preserving
  cAccount1; Contact/Account get a full filters.json incl. cTags)

Lead (built from scratch):
- create Lead<->CTag many-to-many relation via EntityManager (relationName
  cLeadTag, join table c_lead_tag); link normalized to cTags to mirror the
  other three (API auto-prefix had produced cCTags)
- add cTags field, de_DE/en_US labels, clientDefs panel polish (create:false,
  unlink-only row actions), bottomPanelsDetail entry, and filters.json
- CTag side: links.interessenten label de "Interessenten" / en "Leads"

Verified via API/DB: cTags linkMultiple present on all four scopes; Lead
link/CTag.interessenten resolve; Any of / All of / None of filters execute
and return correct results end-to-end; existing data intact.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

espocrm-custom/custom/Espo/Custom/Resources/layouts/Account/filters.json

@@ -0,0 +1,20 @@
+[
+  "assignedUser",
+  "teams",
+  "createdAt",
+  "createdBy",
+  "modifiedAt",
+  "streamUpdatedAt",
+  "type",
+  "industry",
+  "description",
+  "emailAddress",
+  "phoneNumber",
+  "targetLists",
+  "billingAddressCountry",
+  "billingAddress",
+  "shippingAddress",
+  "website",
+  "campaign",
+  "cTags"
+]