fix(typecheck): zero-arg thunk calls, tuple-destructuring let, RuntimeError catch (#128)

[hyperpolymath]

STAGE A (#128/#135). Three compiler-level fixes surfaced by stdlib/testing.affine, taking the AOT stdlib to 14/19:

• ExprApp f [] — a zero-arg call f() on an explicit () -> T thunk (record field / param / lambda) now consumes the unit and yields T. Zero-param fn declarations are bare-return-typed (unaffected); curried/partial application never reaches the empty-arg branch, so peeling one unit arrow is sound.
• StmtLet — each destructured name is generalized at its own component type, not the whole value type. let x = e unchanged; let (a, b) = e now types a/b at their element types (was Unify (Int, (Int,Int))).
• RuntimeError(String) — registered as the interpreter's builtin exception variant (resolve seed + typecheck constructor_env) so try/catch arms in the honest stdlib resolve and type-check.

Plus stdlib/testing.affine: let mut found; tot / float(iterations).

Full suite 233/233, zero regression. Refs #128.

[github-actions]

🔍 Hypatia Security Scan

Findings: 44 issues detected

Severity	Count
🔴 Critical	12
🟠 High	21
🟡 Medium	11

⚠️ Action Required: Critical security issues found!

View findings

[
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    "reason": "Stray AI.a2ml in root -- use 0-AI-MANIFEST.a2ml only",
    "type": "banned",
    "file": "AI.a2ml",
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    "severity": "high"
  },
  {
    "reason": "Superseded by 0-AI-MANIFEST.a2ml",
    "type": "banned",
    "file": "AI.djot",
    "action": "delete",
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  {
    "reason": "Issue in quality.yml",
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    "action": "create",
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  {
    "reason": "Issue in security-policy.yml",
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    "action": "create",
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    "severity": "medium"
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  {
    "reason": "Action hyperpolymath/standards/.github/workflows/governance-reusable.yml@main needs attention",
    "type": "unpinned_action",
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    "action": "pin_sha",
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/example/smoke_driver.ts",
    "action": "flag",
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    "severity": "critical"
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    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/cli.ts",
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    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/mod.ts",
    "action": "flag",
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/lib/compile.ts",
    "action": "flag",
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  {
    "reason": "TypeScript file detected -- banned language",
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    "file": "/home/runner/work/affinescript/affinescript/affinescript-deno-test/lib/runner.ts",
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