Implement story 1.4: location resolution ICAO and address

Adds location.resolve() with ICAO CSV lookup and Nominatim geocoding,
POST /find-location portal route with inline confirmation/error display,
and full test coverage with mocked network calls.

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

src/planemapper/provisioning/location.py

@@ -1 +1,50 @@
-# stub
+import csv
+import importlib.resources
+import logging
+
+import requests
+
+log = logging.getLogger(__name__)
+
+NOMINATIM_URL = "https://nominatim.openstreetmap.org/search"
+_USER_AGENT = "planemapper/0.1 (https://github.com/football2801/planeMapper)"
+
+
+def _lookup_icao(code: str) -> tuple[float, float, str] | None:
+    traversable = importlib.resources.files("planemapper.data").joinpath("airports.csv")
+    with traversable.open("r", encoding="utf-8") as fh:
+        reader = csv.DictReader(fh)
+        for row in reader:
+            if row["ident"] == code:
+                return float(row["latitude_deg"]), float(row["longitude_deg"]), row["name"]
+    return None
+
+
+def _geocode(query: str) -> tuple[float, float, str] | None:
+    resp = requests.get(
+        NOMINATIM_URL,
+        params={"q": query, "format": "json", "limit": 1},
+        headers={"User-Agent": _USER_AGENT},
+        timeout=10,
+    )
+    resp.raise_for_status()
+    results = resp.json()
+    if not results:
+        return None
+    r = results[0]
+    return float(r["lat"]), float(r["lon"]), r["display_name"]
+
+
+def resolve(query: str) -> tuple[float, float, str]:
+    query = query.strip().upper()
+    if len(query) == 4 and query.isalpha():
+        result = _lookup_icao(query)
+        if result is None:
+            raise ValueError("ICAO code not found — try an address instead")
+        log.info("ICAO %s resolved to %s", query, result[2])
+        return result
+    result = _geocode(query)
+    if result is None:
+        raise ValueError("Location not found — try a different search term")
+    log.info("Address '%s' resolved to %s", query, result[2])
+    return result