bring the repo up to org standards

Adopt the standard tooling: a Makefile of thin shims over a full
scripts-to-rule-them-all `script/` set, the canonical `.golangci.yml`
vendored byte-identical from `sneak/prompts`, docker-only linting via
`Dockerfile.lint`, a `Dockerfile` and Gitea workflow that gate every
push, and prettier/editorconfig/dockerignore config.

`make build` pointed at a `cmd/dcfinfo` that is not in the tree and
could never have succeeded; this repo is a library, so `build` is now
the compile check over every package.

Clear the 57 findings the canonical linter config reports on `pkg/dcf`.
Two were real: `findDCFMountPoints` checked a never-assigned `erro`
instead of the error from `findAllMountPoints`, discarding it, and
`privatePath` was computed twice so the first computation was dead.
Mountpoint selection otherwise behaves exactly as before; the defects
that survive are filed as issue #6, not fixed here.

Rename `DCFStore` to `Store` and `DCFObject` to `Object` (with its
`DCFStoreRoot` field to `StoreRoot`), which revive's stutter rule
requires and which the `fs.FS` rework in issue #4 will build on.

Replace the placeholder test with tests over the exported surface.
The filesystem walk stays uncovered: it is reachable only through
`GetDCFStores`, which needs real mounted media.

README keeps its content, reorganised into the required sections and
gaining Entrypoints.

(closes #1)

.golangci.yml

@@ -0,0 +1,34 @@
+version: "2"
+
+# Config schema uses the golangci-lint v2 layout (settings live under
+# linters.settings, not top-level linters-settings) so that the
+# thresholds below are actually applied by golangci-lint >= v2.
+
+run:
+  timeout: 5m
+  modules-download-mode: readonly
+
+linters:
+  default: all
+  disable:
+    # Genuinely incompatible with project patterns
+    - exhaustruct      # Requires all struct fields
+    - depguard         # Dependency allow/block lists
+    - godot            # Requires comments to end with periods
+    - wsl              # Deprecated, replaced by wsl_v5
+    - wrapcheck        # Too verbose for internal packages
+    - varnamelen       # Short names like db, id are idiomatic Go
+  settings:
+    lll:
+      line-length: 88
+    funlen:
+      lines: 80
+      statements: 50
+    cyclop:
+      max-complexity: 15
+    dupl:
+      threshold: 100
+
+issues:
+  max-issues-per-linter: 0
+  max-same-issues: 0