test: move 30 standalone integration tests into suite binaries

Problem: crates/sema/tests had grown back from 42 to 80 top-level files
since the July 2026 consolidation. Each one links as its own ~100 MB test
binary, so every core edit relinked 80 binaries and each worktree carried
~8 GB of test executables.

Cause: the suite convention was only recorded in docs/build-time-report.md,
not in AGENTS.md, so new tests were added as top-level files.

Fix: move the 30 files that need no process-global state (no
sema_otel::testing::install, no env-var or cwd mutation, no in-process
signal handler) into tests/suites/ as modules of the existing *_suite.rs
harnesses. 80 binaries -> 50. `cargo test -- --list` yields the same 5180
leaf test names before and after. Record the convention in AGENTS.md and
fix its stale test-file paths.

Also unify clap features (env, wrap_help): the divan bench dev-dependency
enabled them only in test builds, so cargo build and cargo test rebuilt
clap_builder and the sema binary when switching between them.