refactor: add settings, transport and alias packages (#1122)

Part 1/5 of the tea 1.0 rewrite.

**Stack** (split from #1121; each PR targets `main` and builds, tests and lints on its own — the shipped CLI only changes in part 5):

1. #1122 Toolchain and foundation packages ← this PR
2. #1123 Credentials and Git
3. #1124 Terminal
4. #1125 Services
5. #1126 CLI wiring, docs, removal of the old tree

## Changes

- **build:** require Go 1.27; bump gofumpt and golangci-lint to releases that can read Go 1.27 export data (own commit).
- `internal/clierr`: typed errors and executable exit codes.
- `internal/version`: build version and tags.
- `internal/filelock`: moved unchanged from `modules/filelock`.
- `internal/aliases`: user-defined command aliases.
- `internal/transport`: the HTTP client the Gitea SDK runs on (part 4): token, Sudo and SSH-signature auth, retries for safe reads, connect/TLS/response-header timeouts, typed API errors that keep Gitea's message, and a redacted request log for `--debug`; plus raw requests for `tea api`, signed downloads that follow object-storage redirects, and log streaming.
- `internal/settings`: split `config.yml` / `hosts.yml` with locked transactions, plus remote URL parsing.

Nothing imports these packages yet.

Note: `flake.nix` now asks for `go_1_27`; the pinned nixpkgs in `flake.lock` predates Go 1.27 and still needs a `nix flake update nixpkgs`.
Reviewed-on: https://gitea.com/gitea/tea/pulls/1122
Reviewed-by: TheFox0x7 <95654+thefox0x7@noreply.gitea.com>

internal/filelock/filelock_windows.go

@@ -0,0 +1,48 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build windows
+
+package filelock
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"golang.org/x/sys/windows"
+)
+
+// lockFile acquires an exclusive lock on the file using LockFileEx.
+// It polls with non-blocking LockFileEx until timeout.
+func lockFile(file *os.File, timeout time.Duration) error {
+	deadline := time.Now().Add(timeout)
+	handle := windows.Handle(file.Fd())
+
+	// LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY
+	const flags = windows.LOCKFILE_EXCLUSIVE_LOCK | windows.LOCKFILE_FAIL_IMMEDIATELY
+
+	for {
+		// Lock the first byte (advisory lock)
+		var overlapped windows.Overlapped
+		err := windows.LockFileEx(handle, flags, 0, 1, 0, &overlapped)
+		if err == nil {
+			return nil
+		}
+		if err != windows.ERROR_LOCK_VIOLATION {
+			return fmt.Errorf("LockFileEx failed: %w", err)
+		}
+
+		if time.Now().After(deadline) {
+			return fmt.Errorf("timeout waiting for file lock")
+		}
+		time.Sleep(FileLockPollInterval)
+	}
+}
+
+// unlockFile releases the lock on the file.
+func unlockFile(file *os.File) error {
+	handle := windows.Handle(file.Fd())
+	var overlapped windows.Overlapped
+	return windows.UnlockFileEx(handle, 0, 1, 0, &overlapped)
+}