Upgrade to Go 1.27.3 (#308)

## Summary

Moves the repo from Go 1.27.2 to **Go 1.27.3**.

Go 1.27.3 is a security release with one fix: `crypto/x509` stops
trusting certificate chains through eight eMudhra intermediates whose
private keys were compromised (CVE-2026-111943). Binaries built with
go1.27.2 accept those chains whenever the CA bundle they run with
predates the 2026-10-20 trust-store updates. There are no API or GODEBUG
changes between 1.27.2 and 1.27.3.

The latest release, v0.50.0 (2026-10-26), was built with go1.27.2 and
runs on customer machines with their API keys. Cut a release after
merging so users get a 1.27.3 build.

## Changes

- `go.mod`: `go 1.27.2` -> `go 1.27.3`; the release workflow reads
`go-version-file: go.mod`
- `AGENTS.md`: required Go version

`go mod tidy` changed nothing else.

## Verification

- `go build ./...`, `go vet ./...` and `go test -short ./...`: 9/9
packages pass on unmodified go1.27.3, the same as `main` on go1.27.2.
- `gofmt -l` reports the same files on `main` with go1.27.2 as with
go1.27.3, so this change adds no formatting drift.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Toolchain-only bump with no application code changes; CI already
resolves Go from `go.mod`.
> 
> **Overview**
> Bumps the required Go toolchain from **1.27.2** to **1.27.3** in
`go.mod` and aligns the version called out in `AGENTS.md`. No dependency
or source changes; CI/release workflows that use `go-version-file:
go.mod` will pick up the new version automatically.
> 
> This is a patch-level toolchain update (notably the **1.27.3**
security fix around `crypto/x509` trust for compromised eMudhra
intermediates). A new release build after merge is what ships that fix
in distributed binaries.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
e76a810. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: tnsardesai <18272584+tnsardesai@users.noreply.github.com>

Author: tnsardesai

AGENTS.md

@@ -25,4 +25,4 @@ Be mindful that these operations affect production resources.
 - The Makefile's `lint` target uses `|| true`, so it always exits 0 even when lint issues exist. Pre-existing lint warnings (errcheck, staticcheck) are present in the codebase and expected.
 - The `go-keyring` dependency requires D-Bus and `libsecret` on Linux. These are pre-installed in the Cloud VM.
 - `kernel create` works locally without authentication. Most other commands (`deploy`, `invoke`, `browsers`, etc.) require a `KERNEL_API_KEY` env var or `kernel login` OAuth flow.
-- Go module path is `github.com/kernel/cli`. The project requires Go 1.27.2 (specified in `go.mod`).
+- Go module path is `github.com/kernel/cli`. The project requires Go 1.27.3 (specified in `go.mod`).

go.mod

@@ -1,6 +1,6 @@
 module github.com/kernel/cli
 
-go 1.27.2
+go 1.27.3
 
 require (
 	github.com/Masterminds/semver/v3 v3.4.0