fix: observation timestamps, leaked fields, perf path normalization

- #178: Use strftime ISO 8601 format instead of datetime() for observation
  timestamps in all SQL queries (v3 + v2 views). Add normalizeTimestamp()
  helper for non-v3 paths that may store space-separated timestamps.

- #179: Strip internal fields (decoded_json, direction, payload_type,
  raw_hex, route_type, score, created_at) from ObservationResp. Only
  expose id, transmission_id, observer_id, observer_name, snr, rssi,
  path_json, timestamp — matching Node.js parity.

- #180: Remove _parsedDecoded and _parsedPath from node detail
  recentAdverts response. These internal/computed fields were leaking
  to the API. Updated golden shapes.json accordingly.

- #181: Use mux route template (GetPathTemplate) for perf stats path
  normalization, converting {param} to :param for Node.js parity.
  Fallback to hex regex for unmatched routes. Compile regexes once at
  package level instead of per-request.

fixes #178, fixes #179, fixes #180, fixes #181

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cmd/server/testdata/golden/shapes.json

@@ -1046,44 +1046,6 @@
             },
             "path_json": {
               "type": "string"
-            },
-            "_parsedPath": {
-              "type": "array",
-              "elementShape": {
-                "type": "string"
-              }
-            },
-            "_parsedDecoded": {
-              "type": "object",
-              "keys": {
-                "type": {
-                  "type": "string"
-                },
-                "pubKey": {
-                  "type": "string"
-                },
-                "timestamp": {
-                  "type": "number"
-                },
-                "timestampISO": {
-                  "type": "string"
-                },
-                "signature": {
-                  "type": "string"
-                },
-                "flags": {
-                  "type": "object"
-                },
-                "lat": {
-                  "type": "number"
-                },
-                "lon": {
-                  "type": "number"
-                },
-                "name": {
-                  "type": "string"
-                }
-              }
             }
           }
         }