Addresses two further Greptile findings:
- `_warn_if_db_ahead_of_head` only caught `psycopg.OperationalError`.
Non-connection DB errors (e.g. `InsufficientPrivilege` / 42501 if the
runtime DB user lacks SELECT on `_prisma_migrations`) would propagate
uncaught and crash startup — contradicting the docstring's
"informational only, never blocks" guarantee. Widen the catch to
`psycopg.DatabaseError` so all DB-layer errors are swallowed.
- In the P3009 and P3018 idempotent-recovery paths, the call to
`_resolve_specific_migration(name)` was not wrapped in its own
try/except. Being inside an active `except CalledProcessError`
handler, a new `CalledProcessError` from the resolve call would NOT
re-enter the same handler — it would propagate out as
`CalledProcessError`, past `proxy_cli.py`'s `except RuntimeError`,
crashing startup with an unhandled traceback instead of the intended
clean `sys.exit(2)`. Wrap both call sites to convert to RuntimeError.
Adds unit tests for both behaviors.
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