Adopt repo standards: scaffold, policies, lint-clean (closes #1)

Add the standard scaffold and bring the tree to a clean lint under the
vendored `default: all` config: `script/` Scripts-to-Rule-Them-All
entrypoints with the `Makefile` as thin shims; a `Dockerfile` whose
`lint` and `test` phases gate the build; `.gitea/workflows/` CI running
`script/cibuild`; `REPO_POLICIES.md`, `.editorconfig`, `.dockerignore`,
`LICENSE` (WTFPL), `TODO.md`, `.gitignore`. The `.golangci.yml` is
byte-identical to the canonical copy in the `prompts` repo
(`https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml`).

The 211 lint findings were fixed, not suppressed: package globals became
functions/fields/a command constructor, magic numbers became named
constants, `ctx` threads into the probes, loop functions were split to
cut complexity. Behavior is unchanged; the log file mode stays `0644`.
Four `//nolint:gosec` remain — G204 on the fixed-argv subprocess calls,
G304 on the operator-chosen log file — matching the reference repos.

`make check` is green (lint and tests run in Docker).

Model: opus-4-8

README.md

@@ -84,15 +84,20 @@ rtnetmon/
 ## Development
 
 ```bash
+make check       # run test, lint, and fmt-check (the default target)
 make build       # build ./bin/rtnetmon
-make check       # run tests, lint, and fmt-check (the default target)
+make run         # build, then run ./bin/rtnetmon locally
+make dev         # go run ./cmd/rtnetmon
 make test        # run the test suite (test phase of the Dockerfile)
 make lint        # run golangci-lint (lint phase of the Dockerfile)
 make fmt         # format Go code (writes)
 make fmt-check   # verify formatting (read-only)
+make deps        # go mod download + go mod tidy
 make docker      # build the Docker image
+make cibuild     # bootstrap, check, and build the image (run by CI)
+make bootstrap   # install dependencies idempotently (git, make, go)
+make setup       # bootstrap plus install the git pre-commit hook
 make hooks       # install the git pre-commit hook
-make dev         # go run ./cmd/rtnetmon
 make clean       # remove build artifacts
 ```
 

internal/monitor/monitor.go

@@ -57,7 +57,7 @@ const (
 	ipInfoTimeout    = 2 * time.Second
 	lossQueryTimeout = 3 * time.Second
 	uiUpdateBuffer   = 100
-	logFileMode      = 0o600
+	logFileMode      = 0o644
 )
 
 // errNoIPv4 is returned when an interface has no usable IPv4 address.