Add Codex CLI installer provider

[SrFlipFlop]

Why

Codex CLI was also verified as a working Burp MCP client, but its setup currently requires users to manually edit ~/.codex/config.toml and wire the packaged mcp-proxy-all.jar into a stdio MCP definition.

That makes Codex setup more error-prone than Claude Desktop, especially because the Burp extension needs the proxy jar path and the correct --sse-url arguments. Adding a dedicated installer button makes this configuration reproducible and removes the need for users to hand-edit TOML for the common Burp setup.

What changed

• add a new CodexCliProvider installer
• register an Install to Codex CLI button in the MCP installation panel
• extract or reuse the packaged mcp-proxy-all.jar via ProxyJarManager
• create or update ~/.codex/config.toml
• add or replace the [mcp_servers.burp] table with a stdio configuration pointing to the Burp SSE endpoint through the proxy jar
• preserve unrelated Codex config content when updating the file
• add tests covering config creation and table replacement behavior

Scope

This PR only adds automatic installation for Codex CLI.

It does not:

• add installers for other clients
• change the MCP server runtime behavior
• modify the existing Claude Desktop installer flow

Related issues

• Builds on the client setup work documented in #83.
• Helps with #46 by making one tested client easier to configure.
• Related to #38, which asks for clearer setup outside the Claude Desktop happy path.
• May help users hitting #42 by reducing manual config mistakes around proxy and endpoint setup.

Manual verification

• verified that Codex CLI works against a local Burp MCP server through mcp-proxy-all.jar
• verified installer output writes a valid config.toml entry for mcp_servers.burp
• verified existing Codex config sections are preserved while the Burp section is updated

Tests

• added focused tests for Codex config creation
• added focused tests for Codex table merge/replacement behavior
• ran ./gradlew test