Add Web Vitals performance tracking (LCP, INP, CLS, FCP, TTFB)

End-to-end performance metrics tracking: dedicated database table with
percentile aggregation, tracker collection behind data-perf attribute,
/api/send handling, report API endpoints, and Performance dashboard page
with threshold-based metric cards, time-series chart, and per-page breakdown.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/intl/messages/en-US.json

@@ -44,6 +44,7 @@
     "cities": "Cities",
     "city": "City",
     "clear-all": "Clear all",
+    "cls": "CLS",
     "cohort": "Cohort",
     "cohorts": "Cohorts",
     "compare": "Compare",
@@ -113,6 +114,7 @@
     "exists": "Exists",
     "exit": "Exit page",
     "false": "False",
+    "fcp": "FCP",
     "field": "Field",
     "fields": "Fields",
     "filter": "Filter",
@@ -126,6 +128,7 @@
     "funnels": "Funnels",
     "goal": "Goal",
     "goals": "Goals",
+    "good": "Good",
     "goals-description": "Track your goals for pageviews and events.",
     "greater-than": "Greater than",
     "greater-than-equals": "Greater than or equals",
@@ -137,6 +140,7 @@
     "insight": "Insight",
     "insights": "Insights",
     "insights-description": "Dive deeper into your data by using segments and filters.",
+    "inp": "INP",
     "invalid-url": "Invalid URL",
     "is": "Is",
     "is-false": "Is false",
@@ -157,6 +161,7 @@
     "last-hours": "Last {x} hours",
     "last-months": "Last {x} months",
     "last-seen": "Last seen",
+    "lcp": "LCP",
     "leave": "Leave",
     "leave-team": "Leave team",
     "less-than": "Less than",
@@ -182,6 +187,7 @@
     "my-account": "My account",
     "my-websites": "My websites",
     "name": "Name",
+    "needs-improvement": "Needs improvement",
     "new-password": "New password",
     "none": "None",
     "number-of-records": "{x} {x, plural, one {record} other {records}}",
@@ -208,8 +214,10 @@
     "password": "Password",
     "path": "Path",
     "paths": "Paths",
+    "performance": "Performance",
     "pixel": "Pixel",
     "pixels": "Pixels",
+    "poor": "Poor",
     "powered-by": "Powered by {name}",
     "preferences": "Preferences",
     "previous": "Previous",
@@ -246,6 +254,7 @@
     "save": "Save",
     "save-cohort": "Save cohort",
     "save-segment": "Save segment",
+    "sample-size": "Sample size",
     "screen": "Screen",
     "screens": "Screens",
     "search": "Search",
@@ -303,6 +312,7 @@
     "transfer": "Transfer",
     "transfer-website": "Transfer website",
     "true": "True",
+    "ttfb": "TTFB",
     "type": "Type",
     "unique": "Unique",
     "unique-events": "Unique events",