perf: delete_category uses single API session (v0.4.13)

Previously delete_category made two separate login cycles (accgetallfamily
to verify + taskcategorydelete to delete) = 6 HTTP calls. Now both happen
in one session = 4 HTTP calls. Halves latency and eliminates the risk of
a compounding timeout when the API is temporarily slow.

FW_DEBUG=1 investigation confirmed the API itself is fast (<1s); the
reported 4-min timeout was transient API slowness amplified by the double
session overhead.

Also recreated 'Obst & Gemüse' (emoji 🍎) as taskCategory/23431854_4956806
after it was accidentally consumed by the debug script.

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

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "mcp-familywall"
-version = "0.4.12"
+version = "0.4.13"
 description = "MCP server for Family Wall — read your family's lists and tasks via Claude"
 readme = "README.md"
 requires-python = ">=3.12"