iter cli-diag-human: route WorkspaceLoadError through diagnostic in non-JSON path

Closes P2 todo "CLI human-mode diagnostic surface for
WorkspaceLoadError" surfaced by ct.1.8 tester (2026-05-11).
Pre-iter, non-JSON `ail check` (+8 sibling subcommands) propagated
loader errors via anyhow's Display, producing
`Error: <message>` without the bracketed `[code]` prefix the JSON
path emits.

Fix: new private helper `load_workspace_human(path)` in
crates/ail/src/main.rs that wraps ailang_surface::load_workspace,
threads any WorkspaceLoadError through workspace_error_to_diagnostic,
formats the resulting Diagnostic into a single stderr line
`error: [<code>] <def>: <message>`, and exits non-zero. Pure I/O
errors still propagate as anyhow errors.

Nine call sites swapped to the helper (check non-JSON arm, build,
run, emit-ir, prose, describe, deps, diff, manifest). The JSON arm
of `ail check` keeps its explicit `match` — different output
contract (structured stdout array).

The BareCrossModuleTypeRef Diagnostic message gained the existing
migration-command hint ("Run `ail migrate-canonical-types` to fix
legacy fixtures.") so the ct.1.8 actionable-hint test stays green.
The hint previously rode on WorkspaceLoadError's thiserror Display;
making workspace_error_to_diagnostic the single source for both
JSON and human paths required moving it into the Diagnostic body.

RED test crates/ail/tests/cli_diag_human_workspace_load_error.rs
pins the bracketed-code surface on a missing-import workspace
(tempdir-based fixture; no committed corpus addition).

cargo test --workspace: 565/0/3. clippy + doc: zero warnings.
Roadmap entry struck.

docs/roadmap.md

@@ -214,13 +214,14 @@ context. Pick the next milestone from P1.)_
   into one overlay, or stay split. Surfaced during the
   env-construction unify audit.
   - context: JOURNAL 2026-05-10 ("Audit close: env-construction unify"); closed by iter ctt.1 — DESIGN.md §"Env construction" anchors the split decision.
-- [ ] **\[todo\]** CLI human-mode diagnostic surface for `WorkspaceLoadError` —
-  non-JSON `ail check` routes ct.1 errors via `anyhow`/`thiserror`
-  Display (`Error: <message>`) instead of going through
-  `workspace_error_to_diagnostic`, so the bracketed `[code]` prefix
-  the JSON path carries is missing. Plausibly applies to every CLI
-  subcommand that calls `load_workspace(&path)?` directly.
-  - context: JOURNAL 2026-05-11 ("Iteration ct.1") — surfaced by ct.1.8 tester.
+- [x] **\[todo\]** CLI human-mode diagnostic surface for `WorkspaceLoadError`.
+  Shipped 2026-05-14 as iter cli-diag-human — a new `load_workspace_human`
+  helper in `crates/ail/src/main.rs` routes 9 non-JSON
+  `ailang_surface::load_workspace(&path)?` call sites through
+  `workspace_error_to_diagnostic`, so the bracketed `[code]` prefix is
+  preserved across `ail check`, `build`, `run`, `emit-ir`, `prose`,
+  `describe`, `deps`, `diff`, `manifest`.
+  - context: per-iter journal `docs/journals/2026-05-14-iter-cli-diag-human.md`.
 - [x] **\[todo\]** Retire dead `KindMismatch` arm — `validate_classdefs`'s
   `walk_kind_mismatch` path is structurally unreachable through
   well-formed schema post-ct.1 (the canonical-form validator catches