win32ui: remove manual manager IP editing now that the address comes from enrollment

Component: win32ui (Windows agent tray/config GUI, src/win32/ui/) Depends on: #38940 Rough size: S

Description

#38940 makes the manager address a single endpoint (adr) delivered through an enrollment token, not something an end user is meant to hand-type on an already-deployed agent — implementation restriction 3 removes server rotation, and the whole point of the token/trust-anchor flow is that the verified manager identity comes from enrollment, not from free text typed into a box after the fact.

The Windows tray GUI still predates that model. Its main dialog (src/win32/ui/win32ui.rc:45-52) has an editable Manager IP field (EDITTEXT UI_SERVER_TEXT) and a &Save button (PUSHBUTTON "&Save", IDC_ADD). The IDC_ADD handler in src/win32/ui/os_win32ui.c:131-273 reads that box and calls set_ossec_server() to overwrite the configured manager address directly, with no verification step at all — exactly the free-form edit the new bootstrap flow is designed to prevent.

The same IDC_ADD handler also reads a second field, Authentication key (UI_SERVER_AUTH), decodes a base64 blob and imports it via set_ossec_key() (os_win32ui.c:165-246). That path is unrelated to the address field but shares the same button and WM_COMMAND case, so it has to be pulled apart as part of this change, not just deleted alongside the address editing.

Tasks

• Change the Manager IP control (UI_SERVER_TEXT, win32ui.rc:46) to read-only/disabled, so it only ever displays the currently configured address (sourced the same way gen_server_info() / config_read() populate it today, win32/ui/common.c).
• Remove the &Save button (IDC_ADD, win32ui.rc:51) and the manager-IP-writing part of its handler (os_win32ui.c:131-164, the set_ossec_server() call).
• Decide the fate of the auth-key import path (UI_SERVER_AUTH field + set_ossec_key(), os_win32ui.c:165-246), which today shares the Save button — in coordination with the follow-up enrollment-token issue, since it may be replaced by the token flow rather than just deleted.
• Make sure the read-only address display is refreshed after any re-enrollment (e.g. once the follow-up token-based enrollment issue lands), not just at dialog open.
• Keep &Refresh (IDC_CANCEL) as the way to pull the current values into the read-only fields: it already calls config_read() + gen_server_info() (win32/ui/common.c:22-52), which already repopulates both UI_SERVER_TEXT (manager address) and UI_SERVER_AUTH (key) from config_inst — keep this behavior intentional and covered once Save is gone, rather than an accidental side effect of code that used to also support editing.
• Update any Windows GUI documentation/screenshots that reference the Save button or manual IP editing.

Definition of Done

• The Windows agent tray GUI no longer offers a way to type and save an arbitrary manager address.
• The manager address and key shown in the GUI always reflect the actual configured/enrolled value, and pressing &Refresh re-reads and re-displays both (display-only, no edit path).
• No dead code/controls (IDC_ADD and unused strings) left over from the removed Save flow.