feat: secure skill env setup on load (core #688)

When a skill declares required_environment_variables in its YAML
frontmatter, missing env vars trigger a secure TUI prompt (identical
to the sudo password widget) when the skill is loaded. Secrets flow
directly to ~/.hermes/.env, never entering LLM context.

Key changes:
- New required_environment_variables frontmatter field for skills
- Secure TUI widget (masked input, 120s timeout)
- Gateway safety: messaging platforms show local setup guidance
- Legacy prerequisites.env_vars normalized into new format
- Remote backend handling: conservative setup_needed=True
- Env var name validation, file permissions hardened to 0o600
- Redact patterns extended for secret-related JSON fields
- 12 existing skills updated with prerequisites declarations
- ~48 new tests covering skip, timeout, gateway, remote backends
- Dynamic panel widget sizing (fixes hardcoded width from original PR)

Cherry-picked from PR #723 by kshitijk4poor, rebased onto current main
with conflict resolution.

Fixes #688

Co-authored-by: kshitijk4poor <kshitijk4poor@users.noreply.github.com>

tests/agent/test_redact.py

@@ -141,9 +141,13 @@ class TestRedactingFormatter:
     def test_formats_and_redacts(self):
         formatter = RedactingFormatter("%(message)s")
         record = logging.LogRecord(
-            name="test", level=logging.INFO, pathname="", lineno=0,
+            name="test",
+            level=logging.INFO,
+            pathname="",
+            lineno=0,
             msg="Key is sk-proj-abc123def456ghi789jkl012",
-            args=(), exc_info=None,
+            args=(),
+            exc_info=None,
         )
         result = formatter.format(record)
         assert "abc123def456" not in result
@@ -171,3 +175,15 @@ USER=teknium"""
         assert "HOME=/home/user" in result
         assert "SHELL=/bin/bash" in result
         assert "USER=teknium" in result
+
+
+class TestSecretCapturePayloadRedaction:
+    def test_secret_value_field_redacted(self):
+        text = '{"success": true, "secret_value": "sk-test-secret-1234567890"}'
+        result = redact_sensitive_text(text)
+        assert "sk-test-secret-1234567890" not in result
+
+    def test_raw_secret_field_redacted(self):
+        text = '{"raw_secret": "ghp_abc123def456ghi789jkl"}'
+        result = redact_sensitive_text(text)
+        assert "abc123def456" not in result