Support persistent command deny-rules in permissions-config.json

### Is your feature request related to a problem? Please describe.
`permissions-config.json` (per-directory `tool_approvals`) only supports **allow** rules (`kind: "read" | "write" | "commands" | "mcp" | "memory"`). There is no way to persistently mark a command family (e.g. a specific CLI tool) as always-denied for a given trusted location. The only related mechanism, `--deny-tool`, is a per-invocation CLI flag (see #2722) - it doesn't persist across sessions and has its own matching bugs (denies ALL reads instead of the pattern, bypassable via `shell(cat ...)`).

Users who want to categorically block a whole command family (cloud CLIs, destructive tools, package managers, etc.) across all sessions in a directory currently have no durable option - they must remember to reject the prompt every single time, or avoid the tool being available at all.

### Describe the solution you'd like
Extend the `tool_approvals` schema (or add a sibling array, e.g. `tool_denials`) in `permissions-config.json` to support explicit deny rules scoped by location, symmetric with today's allow rules:

```json
{
"locations": {
"C:\\path\\to\\project": {
"tool_approvals": [ ... ],
"tool_denials": [
{
"kind": "commands",
"commandIdentifiers": ["some-cli"]
}
]
}
}
}
```
- Deny rules should always take precedence over allow rules and over the default "ask" behavior (deny > ask > allow, matching Claude Code's precedence model).
- Should match the full command family (e.g. `some-cli`, `some-cli subcommand`, etc.), not just literal substrings, to avoid the bypass issues described in #2722.
- Ideally manageable via a CLI/slash command too (e.g. `/deny-tool some-cli`), mirroring `/reset-allowed-tools`.

### Describe alternatives you've considered
- `--deny-tool` per invocation - not persistent, and has matching bugs (#2722).
- Manually rejecting prompts every time - error-prone, no durable guarantee.

### Additional context
Related: #2722 (deny-tool matching bugs, no persistent profiles), #307 (closed) Comprehensive Permissions System Improvements Proposal, #179 (globally configurable allowed tools).

Start by tracing permissions-config.json and the existing tool_approvals handling, then inspect the --deny-tool path and related issue #2722 for current matching behavior. Review #307 and determine the accepted scope for persistent location-scoped denials, including precedence, command-family matching, and any /deny-tool integration; done means the behavior is implemented and verified for these cases.

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