fix(security): bound load_octads_jsonl read — panic-attack Critical resurfaced (Refs #104) (#176)

## Summary

The 2026-06-01 panic-attack assail re-run surfaced one **Critical
UnboundedAllocation** at `src/rust/corpus/octad.rs:483`.

PR #145 closed 7 of 8 Critical findings via `bounded_read_corpus_file`
(Refs #104). This 8th call site, `Corpus::load_octads_jsonl`, was added
to the codebase after that sweep and re-introduces the same
`std::fs::read_to_string(path)` pattern that #145 fixed everywhere else.

## Fix

One-line route through the existing helper:

```rust
// before
let raw = std::fs::read_to_string(path)
    .with_context(|| format!("read {}", path.display()))?;

// after
let raw = crate::provers::bounded_read_corpus_file(path)?;
```

Identical pattern to #145 — 64 MiB cap via `MAX_PROOF_BYTES`,
`Read::take(N+1)` discipline, error-not-truncate semantics. Unit tests
already cover the helper (`src/rust/provers/io.rs` lines 107-123).

## Test plan

- [x] `cargo check --lib` (helper visibility — already `pub use`d in
`src/rust/provers/mod.rs:20`)
- [ ] `cargo test --lib corpus::octad` (CI)
- [ ] panic-attack re-run after merge — Critical count should drop from
1 to 0

## Out of scope

- The other 12 High UnsafeCode/UnsafeFFI findings from the 2026-06-01
re-run will be filed as a tracker issue for human triage (matches the
#104 pattern); most are post-#104 FFI additions (`coprocessor/flint.rs`,
`src/zig_ffi/chapel_bridge.zig`, `src/zig/ffi/axiom_spark_bridge.zig`,
`ffi/zig/src/*.zig`) that should land in
`reports/audits/assail-classifications.a2ml` rather than be code-fixed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

src/rust/corpus/octad.rs

@@ -479,8 +479,9 @@ impl Corpus {
     pub fn load_octads_jsonl(path: &Path) -> Result<Self> {
         use std::collections::HashMap as Map;
 
-        let raw =
-            std::fs::read_to_string(path).with_context(|| format!("read {}", path.display()))?;
+        // Bounded read (64 MiB cap via MAX_PROOF_BYTES) — mirrors the
+        // remediation pattern from #145 (Refs #104).
+        let raw = crate::provers::bounded_read_corpus_file(path)?;
 
         let mut corpus = Corpus::default();
         let mut adapter_set: Option<String> = None;