localise chrome, smooth prose, in English and Bengali

The engine now owns the words it puts on a page that the author did not write
(ADR-0034). `internal/render/chrome.go` holds the phrase table, Gregorian month
names and decimal digits per language, keyed phrase-then-language so both forms
sit side by side and a half-translated row is visible while reading. Templates
reach it through `t`, `num` and `day`, registered before parsing so a site
override's blocks may call them too.

The reference theme stops hardcoding English: "Newer", "Page 2 of 2" and every
date now come from the table, while `datetime` attributes stay ASCII because a
parser reads them.

Authored text gets goldmark's typographer and nothing else — quotes, dashes and
ellipses smoothed, code spans untouched because it works on the parsed tree. It
is a parser option rather than a function over a page, so the transforms counter
does not move; state.md now says why, so the next reader does not miscount.

Deliberately absent: relative dates, which need a validity window that only the
cache entry will have, and body widow prevention, which cannot be done safely by
a pass over rendered HTML.

internal/render/templates/page.html

@@ -7,7 +7,7 @@
 {{- if .Index}}
 <nav class="sequence">
 {{- with .Prev}}<a rel="prev" href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.Key}}{{end}}</a>{{end}}
-<span><a href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.URL}}{{end}}</a> {{.Index}} of {{.Count}}</span>
+<span><a href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.URL}}{{end}}</a> {{t $.Lang "position" (num $.Lang .Index) (num $.Lang .Count)}}</span>
 {{- with .Next}}<a rel="next" href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.Key}}{{end}}</a>{{end}}
 </nav>
 {{- else if .Members}}
@@ -15,7 +15,7 @@
 <ol class="archive">
 {{- range .Members}}
 <li><a href="{{.URL}}">{{if .Title}}{{.Title}}{{else}}{{.Key}}{{end}}</a>
-{{- if not .Date.IsZero}} <time datetime="{{.Date.Format "2006-01-02"}}">{{.Date.Format "2 January 2006"}}</time>{{end}}</li>
+{{- if not .Date.IsZero}} <time datetime="{{.Date.Format "2006-01-02"}}">{{day $.Lang .Date}}</time>{{end}}</li>
 {{- end}}
 </ol>
 </nav>