GHSA-4wwp-f6gw-6qm5

### Summary: `IsForbiddenAbsPath()` only blocks `conf/conf.json` by exact match. The TLS private key (conf/key.pem) and CA private key (conf/ca.key) live in the same conf/ directory and are absent from the blocklist. Any authenticated user can retrieve them via POST `/api/file/getFile`.

### Root cause `kernel/util/path_guard.go`, `IsForbiddenAbsPath()` has no entry for TLS key material. The `getFile` handler at kernel/api/file.go:497 skips the blocklist for RoleAdministrator, and in v3.8.1 all authenticated users receive RoleAdministrator (no non-admin role is currently issued to direct API consumers). The files are generated on every boot regardless of whether TLS is active.

### Steps to reproduce: ``` # No token required on a default no-auth-code instance curl -s -X POST http://TARGET:6806/api/file/getFile \ -H "Content-Type: application/json" \ -d '{"path": "/conf/key.pem"}' ``` ``` curl -s -X POST http://TARGET:6806/api/file/getFile \ -H "Content-Type: application/json" \ -d '{"path": "/conf/ca.key"}' ```

**Response:** Raw PEM private key bytes.

<img width="927" height="467" alt="2026-08-19_14-19" src="https://github.com/user-attachments/assets/12e0787f-6bfc-416a-b5ad-a22954e45c48" />

### Impact: On deployments with TLS enabled (--ssl flag or NetworkServeTLS), possession of `key.pem` allows decryption of captured HTTPS traffic. Possession of `ca.key` allows signing certificates trusted by any client that imported SiYuan's locaprompts users to do). The files exist on every installation even whenTLS is currently inactive.

### Prior art: This is the same class of bug as GHSA-9jfx-rc58-h23j (conf.json readable via template render) and GHSA-c8r8-95hg-mp34 (MCP file tool blocklist incomplete). The fix is to add `conf/key.pem`, `conf/ca.key`, `conf/cert.pem`, and `conf/ca.crt` to `IsForbiddenAbsPath()`.