feat(dis): flag forbidden-param permission rules CC silently ignores

Extends the DIS scanner and its shared permission-rules lib with a third
documented Claude Code permission footgun. Verified verbatim against
code.claude.com/docs/en/permissions (fetched 2026-06-19).

CC's Tool(param:value) matching (2.1.178) is off-limits for a tool's own
canonicalizing field — CC ignores such a rule and emits a startup warning,
because e.g. Bash(command:rm *) is bypassable by a compound command. The
forbidden fields: command (Bash/PowerShell), file_path (Read/Edit/Write),
path (Grep/Glob), notebook_path (NotebookEdit), url (WebFetch).

- lib/permission-rules.mjs: new forbiddenParamRule(entry) returning
  { tool, key, hint } or null. Only the param:value form (colon present)
  whose key equals the tool's forbidden field is flagged; Bash(npm:*),
  WebFetch(domain:host), Agent(model:opus), and Bash(command) (no colon)
  are left valid. FORBIDDEN_PARAMS map is the single source of truth.
- DIS: scans allow + deny + ask and splits severity by intent — deny/ask
  hits are false security (medium: the block never applies), allow hits are
  dead config (low: param:value matching is deny/ask-only). Two findings,
  permissions-hygiene, CA-DIS-NNN.
- 11 new tests (7 lib, 4 DIS) + 1 fixture forbidden-param-permissions
  (force-added past .gitignore .claude/). Suite 918 -> 929. Snapshot
  unchanged (SC-5 byte-equal), contamination grep clean, gitleaks clean.
  README/CLAUDE document the broadened DIS mandate; test badge synced.
  self-audit: PASS, configGrade A 97, pluginGrade A 100, scanners 13.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ter3E2JSi1Khgmuf2kady8

tests/fixtures/forbidden-param-permissions/.claude/settings.json

@@ -0,0 +1,17 @@
+{
+  "permissions": {
+    "allow": [
+      "Read(file_path:/etc/passwd)",
+      "Bash(npm:*)",
+      "WebFetch(domain:good.com)"
+    ],
+    "deny": [
+      "Bash(command:rm *)",
+      "Grep(path:/secrets)",
+      "Agent(model:opus)"
+    ],
+    "ask": [
+      "WebFetch(url:http://evil.com)"
+    ]
+  }
+}