feat(skills): add skill config interface + llm-wiki skill (#5635)

Skills can now declare config.yaml settings via metadata.hermes.config
in their SKILL.md frontmatter. Values are stored under skills.config.*
namespace, prompted during hermes config migrate, shown in hermes config
show, and injected into the skill context at load time.

Also adds the llm-wiki skill (Karpathy's LLM Wiki pattern) as the first
skill to use the new config interface, declaring wiki.path.

Skill config interface (new):
- agent/skill_utils.py: extract_skill_config_vars(), discover_all_skill_config_vars(),
  resolve_skill_config_values(), SKILL_CONFIG_PREFIX
- agent/skill_commands.py: _inject_skill_config() injects resolved values
  into skill messages as [Skill config: ...] block
- hermes_cli/config.py: get_missing_skill_config_vars(), skill config
  prompting in migrate_config(), Skill Settings in show_config()

LLM Wiki skill (skills/research/llm-wiki/SKILL.md):
- Three-layer architecture (raw sources, wiki pages, schema)
- Three operations (ingest, query, lint)
- Session orientation, page thresholds, tag taxonomy, update policy,
  scaling guidance, log rotation, archiving workflow

Docs: creating-skills.md, configuration.md, skills.md, skills-catalog.md

Closes #5100

website/docs/user-guide/features/skills.md

@@ -67,6 +67,11 @@ metadata:
     category: devops
     fallback_for_toolsets: [web]    # Optional — conditional activation (see below)
     requires_toolsets: [terminal]   # Optional — conditional activation (see below)
+    config:                          # Optional — config.yaml settings
+      - key: my.setting
+        description: "What this controls"
+        default: "value"
+        prompt: "Prompt for setup"
 ---
 
 # Skill Title
@@ -142,6 +147,24 @@ When a missing value is encountered, Hermes asks for it securely only when the s
 
 Once set, declared env vars are **automatically passed through** to `execute_code` and `terminal` sandboxes — the skill's scripts can use `$TENOR_API_KEY` directly. For non-skill env vars, use the `terminal.env_passthrough` config option. See [Environment Variable Passthrough](/docs/user-guide/security#environment-variable-passthrough) for details.
 
+### Skill Config Settings
+
+Skills can also declare non-secret config settings (paths, preferences) stored in `config.yaml`:
+
+```yaml
+metadata:
+  hermes:
+    config:
+      - key: wiki.path
+        description: Path to the wiki directory
+        default: "~/wiki"
+        prompt: Wiki directory path
+```
+
+Settings are stored under `skills.config` in your config.yaml. `hermes config migrate` prompts for unconfigured settings, and `hermes config show` displays them. When a skill loads, its resolved config values are injected into the context so the agent knows the configured values automatically.
+
+See [Skill Settings](/docs/user-guide/configuration#skill-settings) and [Creating Skills — Config Settings](/docs/developer-guide/creating-skills#config-settings-configyaml) for details.
+
 ## Skill Directory Structure
 
 ```text