feat(config): register bundled-skill API keys in OPTIONAL_ENV_VARS

Adds NOTION_API_KEY, LINEAR_API_KEY, TENOR_API_KEY, and AIRTABLE_API_KEY
to OPTIONAL_ENV_VARS so:

- They persist to ~/.hermes/.env via save_env_value like every other
  key Hermes knows about, instead of being ad-hoc variables the user
  has to hand-edit the dotfile for.
- load_env() / reload_env() populate os.environ from .env on every
  startup — the user sets the key once, skills keep working across
  restarts without losing access.
- hermes setup / hermes config show surface them as known optional
  vars with the correct signup URL (linear.app/settings/api,
  airtable.com/create/tokens, etc.).

These four entries use category="skill" (new) rather than "tool".
tools/environments/local.py auto-adds every category=tool/messaging
entry to _HERMES_PROVIDER_ENV_BLOCKLIST, which stops env passthrough
from leaking provider credentials into the execute_code sandbox
(GHSA-rhgp-j443-p4rf). Skill API keys are the opposite case — the
point is for the agent's subprocess to see them so curl can read
Authorization headers — so they must be outside the blocklist. The
new category is inert for that check.

All four entries are advanced=True: they show up in 'hermes config'
and 'hermes status' displays, but do not nag users who have never
touched those skills during setup checklists.

E2E verified: save_env_value → reload_env → os.environ populated →
skill_view reports setup_needed=False → env_passthrough registers
the key for subprocess inheritance.

hermes_cli/config.py

@@ -1582,6 +1582,44 @@ OPTIONAL_ENV_VARS = {
         "category": "tool",
     },
 
+    # ── Bundled skills (opt-in: only needed if the user uses that skill) ──
+    # These use category="skill" (distinct from "tool") so the sandbox
+    # env blocklist in tools/environments/local.py does NOT rewrite them —
+    # skills legitimately need these passed through to curl via
+    # tools/env_passthrough.py when the user's skill calls out.
+    "NOTION_API_KEY": {
+        "description": "Notion integration token (used by the `notion` skill)",
+        "prompt": "Notion API key",
+        "url": "https://www.notion.so/my-integrations",
+        "password": True,
+        "category": "skill",
+        "advanced": True,
+    },
+    "LINEAR_API_KEY": {
+        "description": "Linear personal API key (used by the `linear` skill)",
+        "prompt": "Linear API key",
+        "url": "https://linear.app/settings/api",
+        "password": True,
+        "category": "skill",
+        "advanced": True,
+    },
+    "AIRTABLE_API_KEY": {
+        "description": "Airtable personal access token (used by the `airtable` skill)",
+        "prompt": "Airtable API key",
+        "url": "https://airtable.com/create/tokens",
+        "password": True,
+        "category": "skill",
+        "advanced": True,
+    },
+    "TENOR_API_KEY": {
+        "description": "Tenor API key for GIF search (used by the `gif-search` skill)",
+        "prompt": "Tenor API key",
+        "url": "https://developers.google.com/tenor/guides/quickstart",
+        "password": True,
+        "category": "skill",
+        "advanced": True,
+    },
+
     # ── Honcho ──
     "HONCHO_API_KEY": {
         "description": "Honcho API key for AI-native persistent memory",