analytics(engine): pure deterministic AnalyticsEngine + models + tests (KC-51 ph1)

Phase 1 of the analytics system (/goal): the framework-independent analysis
engine. Value-type models (MetricDelta, TrendResult, DaySample, WeeklyReport,
MonthlyReport, ...) and AnalyticsEngine with documented formulas (volume,
%change, consistency, trend) and honest degradation (nil/zero/tiny baseline,
new exercise, rest day, outliers via winsorize, unit-dimension compatibility,
divide-by-zero). Calendar math takes an injected Calendar (locale/firstWeekday/
timezone/DST-safe).

AnalyticsEngineTests: 35 XCTest cases. Independently verified by compiling the
engine with swiftc and running a 42-assertion harness — all pass. (Xcode test
target not runnable in this env; assertions mirror the XCTest file.)

Registered the new files via xcodegen. Logs KC-51 phase-1 progress in ISSUES.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

KisaniCal.xcodeproj/xcshareddata/xcschemes/KisaniCal.xcscheme

@@ -1,11 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "1500"
-   version = "1.7">
+   LastUpgradeVersion = "2660"
+   version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
-      buildImplicitDependencies = "YES"
-      runPostActionsOnFailure = "NO">
+      buildImplicitDependencies = "YES">
       <BuildActionEntries>
          <BuildActionEntry
             buildForTesting = "YES"
@@ -27,8 +26,7 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
-      shouldUseLaunchSchemeArgsEnv = "YES"
-      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      shouldUseLaunchSchemeArgsEnv = "YES">
       <MacroExpansion>
          <BuildableReference
             BuildableIdentifier = "primary"
@@ -51,8 +49,6 @@
             </BuildableReference>
          </TestableReference>
       </Testables>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </TestAction>
    <LaunchAction
       buildConfiguration = "Debug"
@@ -74,8 +70,6 @@
             ReferencedContainer = "container:KisaniCal.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </LaunchAction>
    <ProfileAction
       buildConfiguration = "Release"
@@ -93,8 +87,6 @@
             ReferencedContainer = "container:KisaniCal.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
-      <CommandLineArguments>
-      </CommandLineArguments>
    </ProfileAction>
    <AnalyzeAction
       buildConfiguration = "Debug">