fix(hir): perry.define of process.env.* folds at lowering, not just tree-shake (#5009)

[proggeramlug]

Summary

Fixes #5009 — perry.define of process.env.NODE_ENV (and any process.env.*) was silently ignored in every default build. As a result, compiled packages that branch on process.env.NODE_ENV (React, react-reconciler, scheduler, …) selected their development builds, and react-reconciler's dev build then threw TypeError: value is not a function during render — the last wall before yoga for ink (#348).

Root cause (not #4993 as the issue guessed)

#4993 only touched runtime files; process.env.X still lowered to Expr::EnvGet. The real bug is broader: the define was only consulted by the env_fold branch pruner, which is gated on tree_shake — and tree-shaking is off by default (PERRY_TREE_SHAKE=1 / perry.experiments.treeShake: true only). So in a normal build the define did nothing and process.env.NODE_ENV stayed a live runtime EnvGet → js_getenv_value lookup (undefined when unset).

Fix

Fold a defined process.env.<NAME> read to its literal at the single HIR lowering point that would otherwise emit Expr::EnvGet — independent of tree-shaking and in every context (branch conditions, ternaries, closures). esbuild-style define semantics: the define wins over the runtime environment.

• perry-hir/ir/constants.rs — EnvDefine enum + ENV_DEFINES thread-local (mirrors the existing COMPILE_PACKAGES_OVERRIDE pattern; rayon-safe per worker) with set_env_defines / clear_env_defines / env_define_lookup.
• perry-hir/lower/expr_member.rs — env_define_literal() substitutes the literal in both the process.env.X and process.env["X"] arms before emitting EnvGet.
• perry/compile/collect_modules.rs — env_defines_for_lowering() strips the process.env. prefix from ctx.define; installed before each lower_module_full, cleared after.

Composes cleanly with env_fold: the substitution yields a string literal that try_const already folds, so branch-elimination still works under tree-shake; the tree-shake-only node_modules NODE_ENV → "production" default is unchanged. Keys without an explicit define still produce a runtime EnvGet.

Verification

• Reproduced the bug with a react-reconciler-shaped compilePackages fixture; after the fix the production build is selected and the define wins over a conflicting runtime NODE_ENV=development.
• No regression: without a define, runtime env reads work as before; fix(runtime): node:process default import & globalThis.process expose the full process object (#4987) #4993's test_gap_process_import_4987.ts is still byte-identical to node --experimental-strip-types.
• New tests: crates/perry/tests/issue_5009_define_process_env.rs (2 integration) + a unit test for env_defines_for_lowering. All pass.

The secondary item in the issue (react-reconciler's development build hits a value is not a function codegen gap) is out of scope here — production is the target build and now selected.

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