Re-vendor the canonical files from sneak/prompts at dd4027b (closes #213)

Linting and testing become the lint and test phases of the Dockerfile,
and the build stage depends on both. Dockerfile.lint, CHECK_EPOCH and
the tests that checked them are removed. Every docker build in script/
passes --no-cache, and script/cibuild runs script/bootstrap first. A
host without Go gets the go.mod version from script/install-go in
.tool/go, where script/fmt and script/fmt-check also look; fmt-check
reads only the Go files git lists. The image takes its version from the
VERSION build arg or git describe, dev without .git. This repo's own
entries follow the canonical content in .gitignore and .editorconfig.
The golangci-lint v2.14.0 findings are fixed. The rules in CLAUDE.md
move into AGENTS.md. IsDevVersion counts "unknown".

Model: opus-5-5

.gitignore

@@ -1,28 +1,62 @@
-# Binary
-/vaultik
-
-# goreleaser output
-/dist/
-
-# Locally installed pinned tools (script/install-goreleaser)
-/.tool/
-
-# Test artifacts
-*.out
-*.test
-coverage.html
-coverage.out
-
-# IDE
-.vscode/
-.idea/
-*.swp
-*.swo
-
 # OS
 .DS_Store
 Thumbs.db
 
-# Local config for development
+# Editors
+*.swp
+*.swo
+*~
+*.bak
+.idea/
+.vscode/
+*.sublime-*
+
+# Agent scratch (worktrees of this repo, created and destroyed by
+# in-flight tooling). Unanchored: .gitignore patterns already match at
+# every depth, so no prefix is wanted here. This is not a .dockerignore
+# entry and must not be given a `**/` prefix on the way into one.
+.claude/
+
+# Node
+node_modules/
+
+# Secrets. Unanchored like every entry above, so each matches at every
+# depth. Matching is case-sensitive on Linux, so names use character
+# ranges rather than a lowercase form that misses `Server.Key`.
+
+# Environment files. `*.env` covers bare `.env` and the `prod.env`
+# convention. Only the templates `example.env` and `sample.env` are
+# re-included below. A repository that commits any other template adds
+# its own negation after these lines, for example `!.env.example`.
+*.[eE][nN][vV]
+.[eE][nN][vV].*
+.[eE][nN][vV][rR][cC]
+!example.env
+!sample.env
+
+# Private keys and the bundles carrying them.
+*.[pP][eE][mM]
+*.[kK][eE][yY]
+*.[pP]12
+*.[pP][fF][xX]
+[iI][dD]_[rR][sS][aA]
+[iI][dD]_[dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]
+[iI][dD]_[eE][cC][dD][sS][aA]_[sS][kK]
+[iI][dD]_[eE][dD]25519
+[iI][dD]_[eE][dD]25519_[sS][kK]
+
+# Go build and test output.
+*.log
+*.out
+*.test
+coverage.html
+
+# This repo's own host-built artifacts.
+/vaultik
+/dist/
+/.tool/
+
+# Local configs for development; they hold storage credentials.
 local-config.yaml
-dev-config.yaml
+dev-config.yaml