chore: bump pinned rainix to latest

[thedavidmeister]

The `rainix` flake input in `flake.lock` is pinned to rev `f3bdb28f` (2024-05-03). Latest `rainlanguage/rainix` main is `d444279b` (2026-05-19) — roughly two years of drift.

Why bump now

Notable changes upstream since the current pin (chronological, recent first):

• 2024 02 04 refactor pagination #176 — `devShellHook` now skips `npm ci` when the lockfile matches `node_modules/.package-lock.json`. Eliminates the multi-second wait every `nix develop --command …` triggers in this repo.
• bump i9r #174 — declare `workflow_call` secrets on sol reusable workflows
• 2024 02 02 vault balance changes #172 — include foundry-bin in rust-shell (anvil for tests)
• codemirror ext - text editor #171 — drop `pkgs.chromium` from default devShell
• fix(common): compose rainlang with required entrypoints #166 — nixpkgs bump + cargo-expand on PATH
• 2024 01 31 refactor test insta #165 — drop `wasm-bindgen-cli` pin
• 2024 01 31 export csv #164 — upstream `rainix-rs-wasm-test` reusable workflow
• Pagination with end page #159 — remove tauri shell

Suggested approach

```
nix flake lock --update-input rainix
```

and verify:

• `nix develop` still works (now without the `npm ci` on every entry once the lockfile is in sync)
• all CI workflows resolve their reusable workflows correctly
• `rust-shell` has `anvil` available
• no chromium-dependent test paths still reference the dropped pkg

The bump touches `flake.lock` only; no code changes expected. If `rainix-rs-wasm-test` is now upstream, this repo's local copy of the workflow can be retired.

🤖 Generated with Claude Code

[linear]

RAI-619