Add drift test for optimization pass documentation

[bachase]

Problem or motivation

The instruction reference has a drift test that checks C++ opcodes and HIR operation types against docs/opcodes.json. Optimization pass documentation does not have an equivalent guard.

Pass metadata is registered in src/clifft/optimizer/pass_registry.h, while the docs metadata is manually mirrored in docs/macros.py. If a pass is added, removed, renamed, or has its default-enabled status changed, the docs can silently drift.

Proposed solution

Add a focused Python test, similar in spirit to tests/python/test_opcode_docs.py, that verifies pass documentation is complete relative to the C++ pass registry.

Suggested acceptance criteria:

• Parse src/clifft/optimizer/pass_registry.h for registered pass names.
• Check that every registered pass appears in the pass metadata exposed from docs/macros.py or an equivalent docs data source.
• Optionally also check kind/default-enabled metadata if that can be done without making the test brittle.
• The test should fail with an actionable message when docs metadata is missing or stale.

Alternatives considered

A future refactor could move pass docs metadata into a shared structured file, but a small drift test is likely the best first step. It keeps the issue approachable and matches the existing pattern used for opcode documentation.