build: update golangci-lint to v2.12.2 with org-standard v2 config (#96)

Updates golangci-lint to v2.12.2 and sets `.golangci.yml` to the org-standard v2-schema config already deployed across the org's repos. The config change is owner-authorized (see #96 (comment) and #96 (comment)); the same file is being landed as canonical via prompts PR #24 (sneak/prompts#24).

## Changes

- **Commit-pinned installs**: golangci-lint pinned to commit `c0d3ddc9cf3faa61a4e378e879ece580256d76e5` (v2.12.2, released 2026-05-06) in `Dockerfile` and `script/bootstrap`.
- **`.golangci.yml` set to the org-standard v2 config** (sha256 `021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb`), byte-identical to the file used across the org's other repos. Settings live under `linters.settings`, so the `lll`/`funlen`/`cyclop`/`dupl` thresholds are actually applied (under the old hybrid file, v2 silently ignored the top-level `linters-settings` block).
- **Lint fixes** required by the now-active thresholds:
  - `goconst`: shared constants for repeated status/priority/DNS-fixture strings in `internal/watcher/watcher.go` and the notify, state, and watcher tests
  - `dupl`: consolidated duplicated ntfy/slack HTTP-error tests and SendNotification endpoint-error tests behind shared helpers in `internal/notify/delivery_test.go`
  - `lll`: wrapped long test table entries and comments in `internal/config/classify_test.go`, `internal/notify/history_test.go`, `internal/state/state_test.go`, `internal/watcher/watcher_test.go`; shortened one inline nolint justification in `internal/notify/retry.go`
- **`TODO.md`**: Completed Steps entry updated in the same commit.
- Rebased onto current `main` (`f79cd98`); the branch is one clean commit.

## Notes

- v2.12 deprecates the `gomodguard` linter in favor of `gomodguard_v2`. The org-standard config does not disable the deprecated linter, so golangci-lint may emit an informational deprecation warning; this is accepted by the owner and does not affect the exit status (this exact config+code combination was CI-green at `dea7e44`).

## Verification

- `make check` exits 0 (fmt-check, tests, lint)
- `make lint`: 0 issues; no deprecation warning surfaced in the runs performed
- sha256 of `.golangci.yml` at HEAD verified equal to `021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb`

Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #96
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

.golangci.yml

@@ -1,5 +1,9 @@
 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
@@ -12,7 +16,6 @@ linters:
     - depguard         # Dependency allow/block lists
     - godot            # Requires comments to end with periods
     - wsl              # Deprecated, replaced by wsl_v5
-    - gomodguard       # Deprecated, replaced by gomodguard_v2
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
   settings:
@@ -25,25 +28,7 @@ linters:
       max-complexity: 15
     dupl:
       threshold: 100
-  exclusions:
-    generated: lax
-    paths:
-      - third_party$
-      - builtin$
-      - examples$
 
 issues:
   max-issues-per-linter: 0
   max-same-issues: 0
-
-formatters:
-  enable:
-    - gofmt
-    - gofumpt
-    - goimports
-  exclusions:
-    generated: lax
-    paths:
-      - third_party$
-      - builtin$
-      - examples$

TODO.md

@@ -26,11 +26,13 @@ confirm make check still passes.
 # Completed Steps
 
 - 2026-08-07: golangci-lint bumped to v2.12.2 (commit-pinned installs
-  in `Dockerfile` and `script/bootstrap`); `.golangci.yml` migrated to
-  the v2 schema (owner-authorized; becomes the new org canonical), so
-  the lll/funlen/cyclop/dupl thresholds now apply; deprecated
-  `gomodguard` disabled in favor of `gomodguard_v2`; fixed the
-  resulting `goconst`, `dupl`, and `lll` findings
+  in `Dockerfile` and `script/bootstrap`); `.golangci.yml` set to the
+  org-standard v2-schema config used across the org's repos
+  (owner-authorized; same file is being landed as canonical via prompts
+  PR #24), with settings under `linters.settings` so the
+  lll/funlen/cyclop/dupl thresholds apply; fixed the resulting
+  `goconst`, `dupl`, and `lll` findings; the informational `gomodguard`
+  deprecation warning under this config is accepted
 - 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints,
   Makefile shims, README Entrypoints section
 - 2026-02-20: iterative DNS resolver implemented; tests made hermetic