core, ui: per-server roles for self-hosted servers (#7254)

* core, ui: plan per-server roles for self-hosted servers

* core: add per-server roles field to UserServer

* core: add nullable role columns to protocol_servers

* core: persist per-server roles

* core: validate server coverage using per-server roles

* test: cover per-server roles resolution and coverage

* multiplatform: per-server role toggles for self-hosted servers

* ios: per-server role toggles for self-hosted servers

* core: per-server role overrides with per-role defaults

* test: cover three-state per-server role resolution

* fix: derive Eq for ServerRolesOverride

* multiplatform: three-state role dropdowns on saved servers

* ios: three-state role pickers on saved servers

* test: per-server roles independent across two servers

* test: enable names role in name-resolution tests

* style: trim comments in per-server roles code

* chore: rename server_roles migration to 20260716 (last)

* core: per-server roles override operator roles, inherit when unset

* multiplatform: per-server role default inherits from operator

* ios: per-server role default inherits from operator

* refactor(servers): tidy per-server roles per review

- dedup no-operator default into ServerRoles.noOperatorDefault (Kotlin/Swift)
- iOS: move roles-section control flow to the call site via a named gate,
  and parse the server address once instead of up to three times
- Kotlin: collapse redundant derivedState; revert defaultOn->default rename
  for cross-platform parity
- drop unused Hashable conformance on Swift ServerRoles
- add agentServerCfgs test for names inheritance from an operator
- remove no-op enableNamesRole calls from dormant DirectoryTests
- fix ChatClient import ordering

* chore(migration): date server_roles migration 20260720

* only show roles when server is enabled, move section above QR code

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Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>

src/Simplex/Chat/Store/Postgres/Migrations/chat_schema.sql

@@ -1187,7 +1187,10 @@ CREATE TABLE test_chat_schema.protocol_servers (
     user_id bigint NOT NULL,
     created_at timestamp with time zone DEFAULT now() NOT NULL,
     updated_at timestamp with time zone DEFAULT now() NOT NULL,
-    protocol text DEFAULT 'smp'::text NOT NULL
+    protocol text DEFAULT 'smp'::text NOT NULL,
+    role_storage smallint,
+    role_proxy smallint,
+    role_names smallint
 );