fix(security): resolve 6 confirmed vulnerabilities (#273)

[rahmaniramin550-ai]

Summary of Security Remediations

Closes #273

This PR resolves all 6 confirmed security vulnerabilities reported in #273:

1. Vision Image SSRF & Excessive Buffering (src/utils/image.ts)

   • Added validateSafeUrl to reject private IPv4/IPv6, loopback (127.0.0.0/8, ::1), link-local / cloud metadata (169.254.169.254), and internal hostnames.
   • Replaced unbounded res.arrayBuffer() buffering with streaming chunk reading that aborts and throws CLIError immediately if size exceeds MAX_IMAGE_SIZE_BYTES (50 MB), preventing denial of service / memory exhaustion.

2. Speech Subtitle SSRF (src/commands/speech/synthesize.ts)

   • Validates response.data.subtitle_file with validateSafeUrl before attempting download, preventing internal network access if an API response is spoofed or compromised.

3. Media Download SSRF & Safe File Creation (src/files/download.ts)

   • Added destination URL validation rejecting private/loopback/cloud metadata destinations before starting download attempts.
   • Configured temporary download file writer with flags: 'wx' and mode: 0o600 to prevent symlink following and TOCTOU file hijacking.

4. Config Temp-File Symlink Race (src/config/loader.ts)

   • Replaced predictable static config.json.tmp path with unique, cryptographically random temporary filename.
   • Wrote temporary config using flag: 'wx' (O_CREAT | O_EXCL) and mode 0o600 so pre-existing symlinks cannot be overwritten.
   • Added automatic cleanup of temporary files if rename fails.

5. Self-Update Temporary Symlink Overwrite (src/update/self-update.ts)

   • Isolated self-update binary downloads inside a dedicated temporary directory created via mkdtempSync with 0o700 user-only permissions.
   • Set download writer flag to wx with mode: 0o700.
   • Prevented unlinking pre-existing files when opening fails with EEXIST.
   • Guaranteed cleanup of temporary directory in finally block.

6. Authenticated Query & Path Parameter Injection (src/client/endpoints.ts)

   • Applied encodeURIComponent to taskId in videoTaskEndpoint and videoTaskV2Endpoint.
   • Applied encodeURIComponent to fileId in fileRetrieveEndpoint.

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Verification & Tests

• Added 6 dedicated regression test suites:
  • test/utils/network.test.ts (16 passing tests)
  • test/utils/image-security.test.ts (7 passing tests)
  • test/files/download-ssrf.test.ts (5 passing tests)
  • test/commands/speech/synthesize-security.test.ts (1 passing test)
  • test/config/loader-security.test.ts (2 passing tests)
  • test/update/self-update-security.test.ts (1 passing test)
  • test/client/endpoints.test.ts (9 passing tests)
• tsc --noEmit passes with 0 type errors.
• eslint passes with 0 errors.

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Payout Address (USDC / Solana):
BuMURy7R5mkCUtasaAWwvXZReZYmCCANMyUXrRy6CZzo

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