feat: core RPC scanning

[brandonspark]

What:

This PR adds the ability to invoke a command across RPC to semgrep mcp to scan a file, rather than spinning up a whole CLI.

Why:

It's hella faster.

How:

We used the logic that we built out in #80 and added a new command, scanFiles, which allows us to scan some files.

Test plan:

vid.mov

[flaper87]

Is this ready for review?

[liukatkat]

• chore: exclude semgrep interfaces from pyright #94
• feat: core RPC scanning #87 👈 (View in Graphite)
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[flaper87]

See https://semgrepinc.slack.com/archives/C096Y2VR8BG/p1753807150948719

@brandonspark I'd suggest we don't link Slack conversations here since this repo is public and people may not want to sign up for slack to see this.

[liukatkat]

I was about to review and merge this PR now that Semgrep 1.131.0 is out. However, after making a small change (capitalizing the global constants per the discussion in #80), I realized that CI started breaking. I made the following changes to make CI pass:

1. I pinned the version of mcp to 1.12.2. This is because of a non-backwards compatible breaking change that affect the way we can use the FastMcp constructor. We can, alternatively, just update how we use the constructor.
2. Now that we are adding semgrep-interfaces as a submodule to the repo, I made some changes to the workflows and excluded the submodule from the pyright scan.

Since I have made some additional changes, I feel like I can't just merge the change right now, and would love if someone could take a look at this before I merge it to main!

[liukatkat]

See https://semgrepinc.slack.com/archives/C096Y2VR8BG/p1753807150948719

@brandonspark I'd suggest we don't link Slack conversations here since this repo is public and people may not want to sign up for slack to see this.

Updated to a video instead!