fix: auto-correct close model name matches in /model validation (#9424)

* feat(skills): add fitness-nutrition skill to optional-skills

Cherry-picked from PR #9177 by @haileymarshall.

Adds a fitness and nutrition skill for gym-goers and health-conscious users:
- Exercise search via wger API (690+ exercises, free, no auth)
- Nutrition lookup via USDA FoodData Central (380K+ foods, DEMO_KEY fallback)
- Offline body composition calculators (BMI, TDEE, 1RM, macros, body fat %)
- Pure stdlib Python, no pip dependencies

Changes from original PR:
- Moved from skills/ to optional-skills/health/ (correct location)
- Fixed BMR formula in FORMULAS.md (removed confusing -5+10, now just +5)
- Fixed author attribution to match PR submitter
- Marked USDA_API_KEY as optional (DEMO_KEY works without signup)

Also adds optional env var support to the skill readiness checker:
- New 'optional: true' field in required_environment_variables entries
- Optional vars are preserved in metadata but don't block skill readiness
- Optional vars skip the CLI capture prompt flow
- Skills with only optional missing vars show as 'available' not 'setup_needed'

* fix: auto-correct close model name matches in /model validation

When a user types a model name with a minor typo (e.g. gpt5.3-codex instead
of gpt-5.3-codex), the validation now auto-corrects to the closest match
instead of accepting the wrong name with a warning.

Uses difflib get_close_matches with cutoff=0.9 to avoid false corrections
(e.g. gpt-5.3 should not silently become gpt-5.4). Applied consistently
across all three validation paths: codex provider, custom endpoints, and
generic API-probed providers.

The validate_requested_model() return dict gains an optional corrected_model
key that switch_model() applies before building the result.

Reported by Discord user — /model gpt5.3-codex was accepted with a warning
but would fail at the API level.

---------

Co-authored-by: haileymarshall <haileymarshall@users.noreply.github.com>

hermes_cli/model_switch.py

@@ -705,6 +705,10 @@ def switch_model(
             error_message=msg,
         )
 
+    # Apply auto-correction if validation found a closer match
+    if validation.get("corrected_model"):
+        new_model = validation["corrected_model"]
+
     # --- OpenCode api_mode override ---
     if target_provider in {"opencode-zen", "opencode-go", "opencode", "opencode-go"}:
         api_mode = opencode_model_api_mode(target_provider, new_model)