feat(nadia): Expose missing calculator operations as API endpoints

Outcome: done
Changed:
  src/typosaurus_sandbox/presentation/api/v1/calculator.py — added imports (average, median, variance, percentage, logging), ValuesRequest model, PercentageRequest model, and four new endpoint handlers with logging and ValueError → 422 conversion
  tests/test_api.py — added 26 test cases across four new test classes
Verified by: `make verify` — 93 tests, 0 failures, 0 new warnings
Findings:
  - `ValuesRequest` model accepts `values: list[float]` and serves /average, /median, /variance
  - `PercentageRequest` model accepts `value: float, total: float` for /percentage
  - All four endpoints log at DEBUG level on invocation
  - Empty list (average, median, variance) and zero total (percentage) produce HTTP 422 with descriptive detail
Open: none
Confidence: high — 26 new tests pass, zero regressions, pattern matches existing endpoint conventions

Typosaurus-Run: 34b5946ec981488091bee588eb919ff2
Typosaurus-Node: 644d226aefca431c81cf8be8a46d2070
Typosaurus-Agent: @nadia
Refs: #28

src/typosaurus_sandbox/presentation/api/v1/calculator.py

@@ -1,9 +1,13 @@
 # retoor <retoor@molodetz.nl>
 
+import logging
+
 from fastapi import APIRouter, HTTPException
 from pydantic import BaseModel, Field
 
-from typosaurus_sandbox.domain.calculator import add, clamp, clamp_to_byte, subtract
+from typosaurus_sandbox.domain.calculator import add, average, clamp, clamp_to_byte, median, percentage, subtract, variance
+
+logger = logging.getLogger(__name__)
 
 calculator_router = APIRouter(prefix="/api/v1/calculator")
 
@@ -28,6 +32,15 @@ class ClampToByteRequest(BaseModel):
     value: int = Field(ge=-2147483648, le=2147483647)
 
 
+class ValuesRequest(BaseModel):
+    values: list[float]
+
+
+class PercentageRequest(BaseModel):
+    value: float
+    total: float
+
+
 class IntResult(BaseModel):
     result: int
 
@@ -38,11 +51,13 @@ class FloatResult(BaseModel):
 
 @calculator_router.post("/add", response_model=IntResult)
 def calculate_add(body: AddRequest) -> IntResult:
+    logger.debug("add %d + %d", body.left, body.right)
     return IntResult(result=add(body.left, body.right))
 
 
 @calculator_router.post("/subtract", response_model=IntResult)
 def calculate_subtract(body: SubtractRequest) -> IntResult:
+    logger.debug("subtract %d - %d", body.left, body.right)
     return IntResult(result=subtract(body.left, body.right))
 
 
@@ -57,4 +72,46 @@ def calculate_clamp(body: ClampRequest) -> FloatResult:
 
 @calculator_router.post("/clamp-to-byte", response_model=IntResult)
 def calculate_clamp_to_byte(body: ClampToByteRequest) -> IntResult:
+    logger.debug("clamp-to-byte %d", body.value)
     return IntResult(result=clamp_to_byte(body.value))
+
+
+@calculator_router.post("/average", response_model=FloatResult)
+def calculate_average(body: ValuesRequest) -> FloatResult:
+    logger.debug("average of %d values", len(body.values))
+    try:
+        result = average(body.values)
+    except ValueError:
+        raise HTTPException(status_code=422, detail="values list must not be empty")
+    return FloatResult(result=result)
+
+
+@calculator_router.post("/median", response_model=FloatResult)
+def calculate_median(body: ValuesRequest) -> FloatResult:
+    logger.debug("median of %d values", len(body.values))
+    try:
+        result = median(body.values)
+    except ValueError:
+        raise HTTPException(status_code=422, detail="values list must not be empty")
+    return FloatResult(result=result)
+
+
+@calculator_router.post("/variance", response_model=FloatResult)
+def calculate_variance(body: ValuesRequest) -> FloatResult:
+    logger.debug("variance of %d values", len(body.values))
+    try:
+        result = variance(body.values)
+    except ValueError:
+        raise HTTPException(status_code=422, detail="values list must not be empty")
+    return FloatResult(result=result)
+
+
+@calculator_router.post("/percentage", response_model=FloatResult)
+def calculate_percentage(body: PercentageRequest) -> FloatResult:
+    logger.debug("percentage %f of %f", body.value, body.total)
+    try:
+        result = percentage(body.value, body.total)
+    except ValueError:
+        raise HTTPException(status_code=422, detail="total must not be zero")
+    return FloatResult(result=result)
+