feat: add e2e test suite with Robot Framework

Add e2e/ dir with Robot Framework tests for page loading, ban records,
blocklist import, config edit. Add requirements.txt. Update Makefile with
test commands. Update .gitignore, backend docs, testing requirements docs.

e2e/tests/01_page_loading.robot

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+*** Settings ***
+Resource    ${CURDIR}/../../resources/common.resource
+
+*** Test Cases ***
+Page Loads And Shows Navigation
+    New Browser    chromium    headless=${TRUE}
+    New Page    ${FRONTEND_URL}
+
+    # Confirm the page title or root element is present.
+    ${title}=    Get Title
+    Should Not Be Empty    ${title}
+
+    Close Browser

e2e/tests/02_ban_records.robot

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+*** Settings ***
+Resource    ${CURDIR}/../../resources/common.resource
+Resource    ${CURDIR}/../../resources/auth.resource
+
+*** Test Cases ***
+Ban Records Are Visible
+    New Browser    chromium    headless=${TRUE}
+    Login As Admin
+
+    Go To    ${FRONTEND_URL}/bans
+
+    # Basic presence check — the ban table or empty state should be present.
+    ${content}=    Get Page Source
+    Should Not Be Empty    ${content}
+
+    Close Browser

e2e/tests/03_blocklist_import.robot

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+*** Settings ***
+Resource    ${CURDIR}/../../resources/common.resource
+Resource    ${CURDIR}/../../resources/auth.resource
+
+*** Test Cases ***
+Blocklist Import Page Opens
+    New Browser    chromium    headless=${TRUE}
+    Login As Admin
+
+    Go To    ${FRONTEND_URL}/blocklists
+
+    ${content}=    Get Page Source
+    Should Not Be Empty    ${content}
+
+    Close Browser

e2e/tests/04_config_edit.robot

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+*** Settings ***
+Resource    ${CURDIR}/../../resources/common.resource
+Resource    ${CURDIR}/../../resources/auth.resource
+
+*** Test Cases ***
+Config Edit Page Opens
+    New Browser    chromium    headless=${TRUE}
+    Login As Admin
+
+    Go To    ${FRONTEND_URL}/config
+
+    ${content}=    Get Page Source
+    Should Not Be Empty    ${content}
+
+    Close Browser