docs: RISC-V hardware acceleration roadmap for FHE

[Pattermesh]

Summary

• Add docs/RISCV_ACCELERATION.md mapping FHE operations to Tenstorrent Tensix
• Operation mapping: NTT, poly multiply, key switching, bootstrapping
• Architecture: CPU/GPU/TT backend with Rust feature flag
• Phased implementation plan

Status

Draft — for review with @abhicris. Docs-only, no code changes.

Ref: #4, kcolbchain/papers#1

[abhicris]

Welcome to kcolbchain, @Pattermesh — glad you're here. 🌱

Here's what happens from this PR:

1. Our automated review looks for obvious issues (tests, secrets, size) within a couple of hours.
2. If it's clean and CI passes, we merge without back-and-forth.
3. If we need changes, we'll leave a specific comment — not a generic nit. Push another commit and we re-review.

While you wait:

• Run the repo's tests locally (see the repo README.md).
• Keep the PR scoped to one concern — bigger PRs land slower.
• Don't commit tokens or .env contents.

What happens after your first merge

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Thanks for writing the code. We're building this to last.