Add versioned template routes and revision selector

[CMJanina]

Add the versioned template route and dropdown from the first item in #39. /internal/templates/[id]/ shows the latest revision, while /internal/templates/[id]/[rev]/ selects a specific revision. The dropdown follows procens with a latest option and a Versions group.

getTemplateVersion now treats omitted, null, and empty revisions as latest, replacing getCurrentTemplate. check.save rejects empty revisions so saved Checks remain pinned to a revision.

Validation: all 22 tests and the build pass. Checked latest and explicit revision routes, dropdown selection, unknown-revision 404, and empty-revision save rejection.

[github-actions]

🔄 Force-push range-diff

c970b592205a → 8910a226e698

Show range-diff

-:  ------- > 1:  5787112 show created_at on check pages (#40)
-:  ------- > 2:  b6d1e86 rewind: make card values directly editable, remove settings inputs
-:  ------- > 3:  80c2781 rewind: collapse component into a pure astro page
-:  ------- > 4:  7500bd1 rewind: factor shared text-align, drop redundant width on flex items
-:  ------- > 5:  fa338fb rewind: add hint that values are click-to-edit
-:  ------- > 6:  e554f7d Test template collection integrity (#41)
1:  c970b59 ! 7:  8910a22 Add versioned template routes and revision selector
    @@ test/templates.test.ts: import { getCollection } from "astro:content";
      import { readdir } from "node:fs/promises";
      
      test("every template directory has tMeta metadata and vice versa", async () => {
    -@@ test/templates.test.ts: test("every template directory has tMeta metadata and vice versa", async () => {
    - });
    - 
    - const templates: template[] = await getCollection("templates").then(x => x.map(t => t.data));
    -+assert(templates.length > 0, "templates must be loaded");
    - 
    - for (const t of templates) {
    -     test(`${t.id} revisions are unique`, () => {
     @@ test/templates.test.ts: test("kink ids are unique", () => {
              }
          }