Rename GitTally to Werkator

`gitTally` is the name of another product in the git space, so the
rename is a precaution; nothing about what the build system does changes.

The name follows one rule: `Werkator` where it is prose, capitalized
where it is a Kotlin type and its file, lowercase everywhere a machine
reads it — the command, packages, paths, configuration keys and values,
the Gitea check context. Environment variables keep their convention and
are uppercase throughout.

Every configuration file is still found under its pre-rename name
(`ConfigFiles`): `.gittally.yml` at the repository root, in a build
worktree and as committed on a branch, `.git/gittally/.gittally.yml` for
the machine layer. The current name wins where both exist, and the old
file is then ignored rather than merged — two files side by side are a
half-done rename, not a layering. Without the fallback an installation
that updated without renaming would not fail: a configuration that is
not found leaves every setting at its default, so it would come up
looking healthy while having forgotten its credentials and its builds.

`docs/werkator-migrationsplan.md` lists what the fallback does not
cover and has to be moved by hand — above all the state directory
`.git/werkator/`, which holds the build history, the control token and
the worktrees, and has no fallback of its own.

`docs/migration-from-legacy.md` is deleted with this: it mapped the
legacy script's environment variables, and every host it addressed has
long since moved to the YAML configuration.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.werkator.yml

@@ -0,0 +1,37 @@
+server:
+  # Public base URL of this Werkator installation — used for all links posted to Gitea.
+  publicBaseUrl: ""
+
+# Gitea integration for fetching commits and posting build statuses.
+gitea:
+  baseUrl: https://github.com   # base URL of the Gitea instance
+  owner: mhoennig                      # repository owner (user or organisation) for Gitea API (e.g. status checks)
+  repo: werkator                      # repository name
+  statusContext: werkator            # label shown on Gitea commit status checks (default: werkator)
+
+# Build artifact retention.
+artifacts:
+  # number of builds to keep per branch
+  retentionPerBranch: 3
+
+# Controls the branch-polling loop.
+watcher:
+  # max commit age for new origin branches to be pulled automatically
+  newBranchMaxAge: 5d
+
+# Per-branch build configuration.
+# Use "default" as the fallback for all branches not listed explicitly.
+branches:
+  default:
+    # run before each build
+    cleanCommand: rm -rf build
+    # shell command for each build 
+    buildCommand: ./gradlew --console=plain --no-daemon test
+    # directories copied as build artifacts
+    artifactDirs:                                         
+      - build/reports
+    stdoutLog: build.stdout.log   # filename for captured stdout
+    stderrLog: build.stderr.log   # filename for captured stderr
+    autoBuild:
+      enabled: false        # whether to rebuild on schedule
+      times: ["01:00"]      # UTC times HH:MM for scheduled builds