The redundant-annotation gate enforces return types only, not parameters or lambdas

[MelbourneDeveloper]

CLAUDE.md bans every inferable annotation, naming parameters and lambda parameters explicitly:

Never annotate function parameters, return types or lambda parameters when inferable: fn add(a, b) = a + b, not fn add(a: int, b: int) = a + b; |x| => x * 2, not |x: int| => x * 2.

crates/osprey-cli/tests/redundant_annotations.rs enforces the return half only. Its reader finds the arrow before the body and deletes the type after it; a parameter annotation is never examined, so obvious ones survive every gate.

Confirmed removable today: examples/db_postgres/pg_smoke.osp:19 — rewriting status(v: int) as status(v) still parses, still type-checks, still lowers to IR, and reports byte-identical symbols. The corpus has many more of this shape.

The existing oracle transfers unchanged and should be reused rather than reinvented: strip the candidate, then require the program to parse, type-check, lower, produce no undefined symbols, and report a byte-identical outline. Parameters need one extra care the return case does not — deleting one annotation can change what a sibling parameter infers, so candidates must be judged one at a time against the same baseline, never stripped in a batch.

Tracked alongside #215 (the same gate does not sweep ML sources).

Found during review of the enforce-inferable-annotations branch.