fix(mir): resolve user type aliases to their base type for movability

[AkiraTamai]

Summary

Follow-up to #539. mir::movability_from_type only recognizes primitives and a hard-coded list of aliases (Nat, Pos, HumanAge, ...), so any other user alias (type Usd = i64 unit USD;, type Count = Nat;) was treated as Move. Branching on such a parameter and returning it on one path then failed move analysis with conflicting ownership ... alive on one control-flow path but consumed on another.

Fix: MIR lowering and the structured-concurrency ownership check resolve aliases through ModuleEnv before deciding movability.

// mir.rs
pub fn resolve_alias_base(env: &ModuleEnv, name: &str) -> String  // follows `type A = B; type B = i64;`, cycle-safe
pub fn lower_hir_to_mir(hir) -> MirBody { lower_hir_to_mir_with_env(hir, None) }
pub fn lower_hir_to_mir_with_env(hir, module_env: Option<&ModuleEnv>) -> MirBody
// LowerCtx.alias_bases: alias -> base type; alloc_local_with_capability: movability_from_type(alias_bases[ty] ?? ty)

// task_ownership.rs: analyze_task_ownership seeds param types with resolve_alias_base(module_env, ty)

executor.rs passes Some(module_env); LocalDecl::ty still records the alias name (only the movability decision changes). Without an env (unit tests, infer_atom_return_type) behavior is unchanged.

Tests: tests/test_alias_movability.{mm,rs} (branch on Usd/Count params; fails on develop) and task_ownership::tests::copy_alias_consumed_by_siblings_is_allowed.

Link to Devin session: https://app.devin.ai/sessions/2eef5afcd69d4e0ab19ada3b22d5cf7e
Open in Devin Desktop: https://app.devin.ai/desktop/session/2eef5afcd69d4e0ab19ada3b22d5cf7e?variant=devin
Requested by: @AkiraTamai

[devin-ai-integration]

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[devin-ai-integration]

Devin Review found 4 potential issues.

[devin-ai-integration]

📝 Info: Alias cycles remain conservative

resolve_alias_base stops repeated aliases and returns a non-primitive name. Cyclic or unresolved aliases therefore remain Move instead of becoming Copy.

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[devin-ai-integration]

📝 Info: Qualified imports retain alias resolution

Imported types keep qualified and unqualified registrations. A qualified alias can therefore continue through its unqualified base to a primitive.

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[devin-ai-integration]

📝 Info: Legacy lowering remains conservative

lower_hir_to_mir still treats unknown aliases as Move. Production move verification uses the environment-aware entry point; remaining callers only prepare liveness and drops.

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