feat(06-01): add Nitro hook content:file:afterParse for reading-time injection

- Register `content:file:afterParse` hook to inject `wordCount` + `minutes`
  on every parsed markdown content object (D-19: 200 wpm, floor 1 min).
- Import pure util `countWordsInMinimalBody` from app/utils/countWords.
- Guard against non-`.md` files (defensive — hook fires on all sources).
- Values persist in @nuxt/content SQLite DB and are queryable via
  queryCollection thanks to matching Zod fields (content.config.ts).

.planning/STATE.md

@@ -3,8 +3,8 @@ gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
 status: Context gathered — ready for /gsd-plan-phase 6
-last_updated: "2026-04-21T23:11:57.514Z"
-last_activity: 2026-04-21
+last_updated: "2026-04-22T06:55:05.535Z"
+last_activity: 2026-04-22
 progress:
   total_phases: 8
   completed_phases: 3
@@ -26,7 +26,7 @@ progress:
 Phase: Phase 6 — Blog Pages
 Plan: —
 Status: Context gathered — ready for /gsd-plan-phase 6
-Last activity: 2026-04-21
+Last activity: 2026-04-22
 Resume file: .planning/phases/06-blog-pages/06-UI-SPEC.md
 
 ## Accumulated Context