Re-vendor the canonical files from sneak/prompts at e3f79c4 (closes #221)

The dotfiles, REPO_POLICIES.md and the standard scripts are fetched
whole from sneak/prompts e3f79c4, with pixa's own entries kept after
them. Check builds pass a new CACHEBUST build argument instead of
--no-cache, and every Dockerfile stage declares it first, so every RUN
step still runs while Go's build cache is kept. Lint runs golangci-lint
v2.14.0, and the test phase runs on the Debian Go image. Of the two new
lint findings, one is fixed and one (gosec G703 on the fixed config file
locations) is suppressed. The agent guidance moves unchanged from
CLAUDE.md to AGENTS.md.

Deviation: the workflow keeps its docker-smoke step while issue 203
waits on the owner.

Model: opus-5-5

TODO.md

@@ -18,7 +18,7 @@
 
 pre-1.0. No git tags exist. The `1.0.0` milestone is in progress; work lands on
 `next`, and `main` receives only the milestone PR that the owner merges. `next`
-is at the canonical `golangci-lint` v2.12.2 config and is green. Recent work
+is at the canonical `golangci-lint` v2.14.0 config and is green. Recent work
 extracted the internal/magic, internal/allowlist, internal/httpfetcher, and
 internal/signature packages. The gosec findings from the 2026-07-06 survey are
 resolved. The disk cache is now size-bounded with LRU eviction
@@ -30,6 +30,26 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-15 the canonical files are re-vendored from `sneak/prompts` commit
+  `e3f79c4` (closes #221): `.dockerignore`, `.editorconfig`,
+  `.gitea/workflows/check.yml`, `.gitignore`, `.golangci.yml`,
+  `.prettierignore`, `.prettierrc`, `REPO_POLICIES.md` and the standard scripts
+  are its copies. pixa's own entries follow the standard part: `/bin`, `/data`
+  and the local config files in `.dockerignore`; Go's `*.log`, `*.out` and
+  `*.test`, `vendor/`, the binaries, `/data/`, `*.sqlite3` and the local config
+  files in `.gitignore`. The workflow keeps its `script/docker-smoke` step while
+  https://git.eeqj.de/sneak/pixa/issues/203 is open. The scripts pass a new
+  `CACHEBUST` build argument in place of `--no-cache`, and every `Dockerfile`
+  stage declares it first, so every `RUN` step still runs on every build while
+  Go's build cache, mounted on the steps that compile, is kept; both `go test`
+  runs keep `-count=1`. The lint and test builds write no image. The lint phase
+  runs golangci-lint v2.14.0, the test phase runs on the Debian Go image, and
+  the build stage marks `/src` safe for git. `script/bootstrap`, `script/fmt`
+  and `script/fmt-check` use the node on the `PATH` only when it has the pinned
+  major version. Of golangci-lint v2.14.0's two findings, an unused `nolint`
+  directive is removed, and gosec's new path check is marked as not applying to
+  the fixed config file locations. The agent guidance moves unchanged from
+  `CLAUDE.md` to a root `AGENTS.md`, where `REPO_POLICIES.md` keeps it.
 - 2026-10-15 the request metrics record any method that is not a standard one as
   `other` (closes #274): their `method` label was each request's method as sent,
   and Go's HTTP server accepts any method name, so a client sending made-up