perf(startup): file runs reuse the stdlib typecheck-env cache (perf plan Phase 3)

[Ch4s3]

Phase 3 of docs/superpowers/plans/2026-08-23-interpreter-and-repl-jit-performance.md (sequencing Gate G3, Lane P).

march file.march (and --compile, which shares the typecheck site) no longer re-typechecks all 116 stdlib modules per run: check_module_full seeds from the existing get_stdlib_tc_env CLI cache (own namespace, keyed by compiler BLAKE3 identity + stdlib content hash — deliberately NOT the REPL's cache file, whose env is built by a different, error-tolerant fold). Startup: ~1.0-1.2 s cold → ~0.28-0.36 s warm.

Guardrails, from review:

• a user module shadowing a stdlib module bypasses the cache entirely (no read, no write) and takes the pre-existing from-scratch check — the seeded env would be degraded; regression test proves the pre-fix cache pollution (fail-first against the unfixed binary, independently reproduced by the re-reviewer)
• new tcenv_cli_cache suite pins cold/warm --emit-llvm IR byte-identity under an isolated HOME
• march warm-cache now warms this cache too

Suites: compiler 936 / eval 273 / codegen 589 — all green at head; user-file diagnostics byte-identical cold vs warm vs pre-change binary; stdlib-heavy compiled IR byte-identical across all three.