lint: drive baseline to zero, drop only-new-issues gate

Cleanup pass over the repo so CI can enforce lint going forward
without the only-new-issues escape hatch:

* gofumpt -w across the tree (31 hits, all formatting)
* misspell --fix (25 hits, US-locale spelling) — but reverted on
  api.JobCancelled = "cancelled" since that literal is the wire +
  DB CHECK constraint value, plus matched the case in store/fleet.go
  back to "cancelled" and added //nolint:misspell on both for the
  next time someone reaches for the auto-fix
* Wrap every `defer rows.Close()` / `defer stmt.Close()` /
  `defer res.Body.Close()` in `defer func() { _ = .Close() }()`
  to satisfy errcheck without losing the close itself
* websocket.Dial callers (1 prod, 4 tests) now capture + close the
  upgrade response Body — coder/websocket can return res with a nil
  Body on success, so the test deferred-closes guard against that
* Annotate the two genuine-by-design nilerr cases with //nolint
  comments explaining why nil-on-error is the contract (cookie
  missing = no session; ctx cancelled mid-backoff = clean shutdown)
* Add brief godoc on the 10 exported const groups + types that
  revive flagged (api.HostOS/HostArch/JobKind/JobStatus/LogStream/
  ErrorCode, restic.EventKind, store.Role, web.FS)
* Drop the unused (*Server).userByID method
* Inline the unparam baseView(active) — every UI page is under
  the dashboard primary nav today

Result: `golangci-lint run ./...` reports 0 issues. CI lint job
no longer needs only-new-issues: true; X-06 follow-up entry in
tasks.md removed.

internal/server/ws/handler.go

@@ -42,14 +42,14 @@ type HandlerDeps struct {
 // enrollment) before the WS upgrade.
 //
 // Lifecycle:
-//   1. Bearer token resolves to a Host row.
-//   2. Upgrade.
-//   3. First message must be `hello`; protocol_version checked here.
-//   4. Loop: read messages, dispatch by type. Heartbeats touch the
-//      host row; job/log/repo messages forward to the relevant
-//      handlers (TODO: lands with P1-18 onward).
-//   5. On Read error or context cancel, mark host offline, unregister
-//      from the hub.
+//  1. Bearer token resolves to a Host row.
+//  2. Upgrade.
+//  3. First message must be `hello`; protocol_version checked here.
+//  4. Loop: read messages, dispatch by type. Heartbeats touch the
+//     host row; job/log/repo messages forward to the relevant
+//     handlers (TODO: lands with P1-18 onward).
+//  5. On Read error or context cancel, mark host offline, unregister
+//     from the hub.
 func AgentHandler(deps HandlerDeps) stdhttp.Handler {
 	return stdhttp.HandlerFunc(func(w stdhttp.ResponseWriter, r *stdhttp.Request) {
 		host, ok := authenticateAgent(r, deps.Store)
@@ -204,7 +204,7 @@ func dispatchAgentMessage(ctx context.Context, c *Conn, hostID string, env api.E
 			string(p.Status), p.ExitCode, p.Stats, errMsg, p.FinishedAt); err != nil {
 			slog.Warn("ws: mark job finished", "job_id", p.JobID, "err", err)
 		}
-		// repo_initialised_at projection has been removed — auto-init
+		// repo_initialized_at projection has been removed — auto-init
 		// at host enrolment makes "is the repo init'd" derivable from
 		// the latest init job's status, no separate column needed.
 		if deps.JobHub != nil {