fix(server): display uvicorn lifecycle logs without an error logger name

[AlexStocks]

Which issue or RFC does this PR close?

N/A — discovered during local usage; no tracking issue exists.

Rationale for this change

uvicorn hardcodes uvicorn.error as its lifecycle logger name, which mostly
carries INFO startup lines but reads like an error channel. New users routinely
misread startup logs such as INFO uvicorn.error Started server process as an
error. The Logger.name attribute is read-only, so the fix rewrites the record
name in the display layer only.

What changes are included in this PR?

• src/powercontext/server/logging.py: add _UvicornDisplayNameFilter,
  registered in the dictConfig and attached to the uvicorn.error logger
  (attached to the logger, not the shared handler, so powercontext's own
  loggers are unaffected). It rewrites record.name to uvicorn for display;
  the logger tree, level routing, and any filtering keyed on the original name
  are untouched.
• tests/test_server_logging.py: add 2 unit tests — the rewrite makes the JSON
  formatter emit "logger":"uvicorn", and other logger names are left untouched.

Are there any user-facing changes?

Display-only: server startup/shutdown logs now render as INFO uvicorn ...
instead of INFO uvicorn.error .... No API, config, or persisted format
changes. JSON-formatted logs emit "logger":"uvicorn" as well. Real errors
still render as ERROR uvicorn ....

How was this change tested?

• uv run python -m pytest tests/test_server_logging.py: 6 passed
• uv run ruff check src/powercontext/server/logging.py tests/test_server_logging.py: passed
• Manual: started the server and verified startup/shutdown lines render as
  INFO uvicorn ...; a simulated error still renders as ERROR uvicorn ...

AI usage statement

An AI assistant (WorkBuddy) was used to implement the filter and draft this PR
description; the implementation was validated locally with tests and manual
runs.

[Teingi]

LGTM