feat: add fuzzing targets for untrusted input parsers (#835)

* feat: add fuzzing targets for untrusted input parsers

Add cargo-fuzz infrastructure with 5 fuzz targets exercising
security-critical code paths:

- fuzz_safety_sanitizer: Aho-Corasick + regex injection detection
- fuzz_safety_validator: Input validation (length, encoding, patterns)
- fuzz_leak_detector: Secret leak scanning (API keys, tokens)
- fuzz_tool_params: Tool parameter JSON validation
- fuzz_config_env: TOML/JSON config parsing

Each target exercises real IronClaw business logic with invariant
assertions. Includes corpus directories and setup documentation.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: improve fuzz targets to exercise real IronClaw code paths

- fuzz_config_env: exercise SafetyLayer end-to-end (sanitize, validate,
  policy check) instead of generic TOML/JSON parsing
- fuzz_tool_params: add validate_tool_schema coverage alongside
  validate_tool_params
- Add "fuzz" to workspace exclude in root Cargo.toml
- Update README descriptions to match actual target behavior

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: replace redundant detect() call with meaningful invariant assertion

Replace the double sanitize()+detect() call with an assertion that
critical severity warnings always trigger content modification.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: rewrite fuzz_config_env to exercise IronClaw safety code directly

Replace SafetyLayer wrapper usage with direct Sanitizer, Validator, and
LeakDetector instantiation and invocation. Adds meaningful consistency
assertions (non-empty output, valid-means-no-errors, scan/clean agreement).
Removes the config construction that was only exercising struct instantiation.

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

Cargo.toml

@@ -14,6 +14,7 @@ exclude = [
     "tools-src/google-slides",
     "tools-src/slack",
     "tools-src/telegram",
+    "fuzz",
 ]
 
 [package]